Engineering 
Library 


Copies  of  this  report  m£y  be  purchased 
at  one  dollar  eaoh  from  the  Secretary  of  . 
the  American  Institute  of  Electrical  Engi- 
neers, 33  West  39th  Street,  New  York,  N.Y. 


REPORT 

OF  THE 

AMERICAN  COMMITTEE 
ON  ELECTROLYSIS 

1921 


i?C     ->* 


Engineering 

y.P-ary 


COMMITTEE 

American  Institute  of  Electrical  Engineers 
BION  J.  ARNOLD,  Chairman,  Chicago,  Illinois. 

N.  A.  CARLE,  Newark,  New  Jersey. 

F.  N.  Waterman,  New  York,  N.  Y. 

American  Electric  Railway  Association 
L.  P.  CRECELIUS,  Cleveland,  Ohio. 

W.  J.  HARVIE,  Syracuse,  N.  Y. 

G.  W.  VAN  DERZEE,  Milwaukee,  Wisconsin. 

American  Railway  Engineering  Association 

E.  B.  KATTE,  New  York,  N.  Y. 
MARTIN  SCHREIBER,                         Newark,  New  Jersey. 
W.  M.  VANDERSLUIS,                        Chicago,  Illinois. 

National  Electric  Light  Association 
L.  L.  ELDEN,  Boston,  Mass. 

D.  W.  ROPER,  Treasurer,  Chicago,  Illinois. 
PHILIP  TORCHIO,  New  York,  N.  Y. 

American  Gas  Association 

WALTER  C.  BECKJORD,  New  York,  N.  Y. 

CHARLES  F.  MEYERHERM,  New  York,  N.  Y. 

H.  C.  SUTTON,  Philadelphia,  Pa. 

Natural  Gas  Association  of  America 
FORREST  M.  TOWL,  New  York,  N.  Y. 

THOMAS  R.  WEYMOUTH,  Oil  City,  Pa. 

S.  S.  WYER,  Columbus,  Ohio. 

American  Telephone  and  Telegraph  Company 
A.  P.  BOERI,  New  York,  N.  Y. 

F.  L.  RHODES,  New  York,  N.  Y. 
H.  S.  WARREN,  New  York,  N.  Y. 

American  Water  Works  Association 
ALFRED  D.  FLINN,  New  York,  N.  Y. 

NICHOLAS  S.  HILL,  JR.,  New  York,  N.  Y. 

E.  E.  MINOR,  New  Haven,  Conn. 

National  Bureau  of  Standards 

BURTON  McCoLLUM,  Washington,  D.  C. 

DR.  E.  B.  ROSA,*  Secretary,  Washington,  D.  C. 

E.  R.  SHEPARD,            -  Washington,  D.  C. 


*  Deceased. 


6  PREFACE 

organizations  they  represent  will  aid  materially  in  reducing  the 
destructive  effects  due  to  electrolysis. 

The  Committee,  through  its  Research  Subcommittee,  has 
established  a  close  working  relationship  with  the  National  Bureau 
of  Standards,  which  has  been  distinctly  advantageous. 

The  Committee  regrets  to  chronicle  the  death  in  Washington 
on  May  17,  1921,  of  its  secretary,  Dr.  Edward  B.  Rosa,  Chief 
Physicist  of  the  National  Bureau  of  Standards,  one  of  its  most 
efficient  and  esteemed  members. 

October,  1921. 

BION  J.  ARNOLD, 

Chairman. 


TABLE  OF  CONTENTS 
CHAPTER  1.     Principles  and  Definitions 

Page 

A.  Electrolysis  in  General: 

1.  Electrolysis 15 

2.  Electrolyte,  Electrode,  Anode,  and  Cathode 15 

3.  Amount  of  Chemical  Action 15 

4.  Cause  of  Current  Flow 16 

5.  Electrolysis  by  Local  Action 16 

6.  Anodic  Corrosion 16 

7.  Secondary  Reactions 16 

8.  Cathodic  Corrosion 17 

B.  Electrolysis  of  Underground  Structures. 

9.  General 17 

10.  Self  Corrosion 17 

11.  Acceleration  of  Local  or  Self  Corrosion 17 

12.  Stray  Current 18 

13.  Anodic  and  Self  Corrosion 18 

14.  Coefficient  of  Corrosion 18 

15.  Passivity 18 

16.  Polarization  Voltage 18 

17.  Alternating  or  Frequently  Reversed  Direct  Currents 19 

18.  Action  on  Underground  Metallic  Structures 19 

19.  Electrolysis  Mitigation ".  / 19 

20.  Electrolysis  Survey 20 

2 1 .  Overall  Potential  Measurements ' 20 

22.  Potential  Gradient 20 

23.  Potential  Difference. ; 21 

24.  Arithmetical  Average 21 

25.  Algebraic  Average 21 

26.  Positive  and  Negative  Areas 21 

27.  Drainage  System 21 

28.  Uninsulated  Track  Feeder  System 22 

29.  Insulated  Negative  Feeder  System 22 

CHAPTER  2.    Design,  Construction,  Operation  and  Maintenance 

1.  Measures  Tending  both  to  Railway  Economy  and  the  Reduction 

of  Stray  Current 24 

2.  Measures  Employed  Solely  for  Electrolysis  Prevention 24 

(a)  Applicable  to  Railways. 

(b)  Applicable  to  Affected  Structures. 

(c)  Interconnection   of   Affected    Structures   and  Railway 

Return  Circuit. 

I.  RAILWAYS 

A.  Features  Which  Affect  Electrolysis  Conditions. 

1.  Track  Construction  and  Bonding 25 

(a)   Importance  of  Rail  Circuit 25 


CONTENTS 

Page 

(b)  Rail  Bond  Resistance  and  Tests 25 

(c)  Types  of  Bonds 26 

Soldered  Bonds 26 

Brazed  or  Welded  Bonds 26 

Resistance  Weld 26 

Electric  Arc  Process 27 

Oxy-Acetylene    Process 27 

Pin  Expanded  Terminal  Bonds 27 

Compressed  Terminal  Bonds 27 

(d)  Welded  Rail  Joints 28 

Electric  Rail  Welding 28 

Arc  Welding 28 

Cast  Welding 28 

Thermit  Process 28 

(e)  Cross-Bonding 29 

(f )  Special  Track  Work  Bonding 29 

(g)  Bonding  Tracks  with  Signal  Systems 30 

(h)  Conductivity  and  Composition  of  Rails 30 

2.  Track  Insulation 31 

(a)  Degrees  of  Insulation 31 

Substantial  Insulation 31 

Partial  Insulation 31 

(b)  Leakage  to  be  Expected 32 

3.  Reinforcement  of  Rail  Conductivity 32 

4.  Power  Supply 33 

(a)  High  Voltage  d.  c.  Railways 34 

(b)  Source  of  Stray  Currents 34 

(c)  Relation  of  Feeding  Distance    to  Stray  Currents  and 

Overall  Voltages 38 

(d)  Economic  Considerations  Involved  in  Additional  Supply 

Stations 42 

(e)  Automatic  Substations 44 

(f)  Location  of  Supply  Stations 46 

(g)  Alternating  Current  Systems 46 

5.  Interconnection  of  Tracks. 47 

B.  Features  of  Railway  Construction  and  Operation  Employed  for 

Electrolysis  Mitigation. 

1 .  Insulated  Negative  Feeder  System 49 

(a)  Description 49 

(b)  Application  of  Insulated  Negative  Feeders 53 

Application  to  Interurban  Lines 55 

(c)  Negative  Boosters 57 

2.  Three-Wire  System 57 

(a)  Description 57 

(b)  Insulation  of  Trolley  Sections 59 

(c)  Costs 59 

(d)  Difficulties  and  Limitations 60 

(e)  Practicability 61 

(f )  Extent  of  Adoption 62 


CONTENTS  9 

Page 
B.  Features  of  Railway  Construction  (continued) 

3.  Reversed  Polarity  Trolley  System 62 

4.  Periodic  Reversal  of  Trolley  Polarity ....  63 

5.  Double  Contact  Conductor  Systems 65 

II.  UNDERGROUND    STRUCTURES    SUBJECT    TO    INJURY    BY 

STRAY  CURRENTS 

A.  Location  with  Respect  to  Tracks. 

B.  Cable  Systems. 

1.  Avoidance  of  Accidental  Contacts  with  Other  Structures.  .  .  66 

2.  Conduit  Construction 67 

(a)  Signal  Cables 67 

(b)  Power  Cables 68 

3.  Surface  Insulation 69 

4.  Insulating  Joints 70 

C.  Pipe  Systems 

1 .  Surface  Insulation 71 

2.  Insulating  Joints 74 

(a)  New  Work 74 

(b)  Cement  Joints 76 

(c)  Leadite  and  Metallium 76 

(d)  Dresser  Couplings 78 

(e)  Special  Insulating  Joints 78 

(f )  Insulating  Joints  Applied  to  Existing  Pipe  Lines 78 

3.  Shielding 79 

III.  MEASURES  INVOLVING  INTERCONNECTION  OF  AFFECTED 

STRUCTURES  AND  RAILWAY  RETURN  CIRCUIT 

A.  Electrical  Drainage  of  Cable  and  Pipe  Systems •  81 

1.  Drainage  of  Cable  Sheaths 83 

(a)  Method  of  Draining  Cables 83 

(b)  Heating  Effect  of  Stray  Current  on  Cable  Sheaths 84 

2.  Difference  Between  Cable  Drainage  and  Pipe  Drainage 88 

3.  Application  of  Drainage  to  Pipes 90 

(a)  Maintaining  Pipes  Negative  to  Earth 90 

(b)  Effect  of  Pipe  Drainage  on  Current  Interchange 90 

(c)  Effects  of  Different  Kinds  of  Pipes  and  Joints 92 

SUMMARY  OF  GOOD  PRACTICE. 

A.  Railways 92 

1.  Track  Construction  and  Bonding 92 

2.  Track  Insulation 93 

3.  Reinforcement  of  Rail  Conductivity 93 

4.  Power  Supply 94 

5.  Interconnection  of  Tracks :  94 

6.  Insulated  Negative  Feeder  System 94 

7.  Three-wire  System 95 

8.  Reversed  Polarity  Trolley  System 95 

9.  Periodic  Reversal  of  Trolley  Polarity 96 

10.  Double  Contact  Conductor  Systems 96 

11.  Alternating  Current  Systems 96 


10  CONTENTS 

Page 

B.  Affected  Structures. 

1.  Location  with  Respect  -to  Tracks 96 

2.  Avoidance  of  Contact  with  Pipes  and  Other  Structures 96 

3.  Conduit  Construction 97 

4.  Insulating  Joints  in  Cable  Sheaths 97 

5.  Surface  Insulation  of  Pipes  and  Cables 97 

6.  Insulating  Joints  in  Pipes 97 

7.  Shielding 98 

C.  Interconnection   of    Affected    Structures   and    Railway   Return 

Circuit. 

1.  Cable  Drainage 98 

2.  Pipe  Drainage 99 

CHAPTER  3.    Electrolysis  Surveys 
I.  INTRODUCTION 

A.  Purpose  and  Scope  of  Electrolysis  Surveys. 

1.  Purpose  of  Electrolysis  Surveys 100 

2.  Difficulty  of  Standardizing  Survey  Procedure 100 

3.  Information  Obtainable  by  Electrolysis  Surveys 100 

B.  Types  of  Surveys 101 

C.  General  Preliminary  Data. 

1.  Data  on  Underground  Structures 102 

2.  Data  on  Railway  Systems 102 

D.  Cooperation  in  Making  Surveys 102 

II.  ELECTRICAL  MEASUREMENTS 

A.  Voltage  Surveys 103 

1.  Measurement  of  Maximum  Potential  Drop  Along  Railways..  104 

(a)  Importance  of  Maximum  Potential  Drop  Measurements.  104 

(b)  Procedure  in  Making  Maximum  Drop  Measurements.  .  104 

2.  Potential  Gradient  Measurements 106 

(a)  Scope  of  Term 106 

(b)  Measurement  of  Potential  Gradients  in  Tracks 106 

3.  Measurement  of  Potential  Differences 107 

(a)  Purpose  of  Measurement  of  Potential  Differences 107 

(b)  Procedure  in  Making  Measurements  of  Potential  Differ- 
ences    107 

B.  Current  Surveys. 

1.  Scope  and  Importance  of  Current  Surveys 108 

2.  Measurement  of  Currents  in  Feeders  and  Rails 109 

(a)  Purpose  of  Measuring  Feeder  and  Rail  Currents 109 

(b)  Procedure  in  Measuring  Current  in  Feeders  and  Rails .  109 

3.  Measurement  of  Currents  in  Pipes  and  Cable  Sheaths 110 

(a)  Purpose  and  Importance  of  Pipe  Current  Measurements.  110 

(b)  Selection  of  Points  of  Measurement 110 

(c)  Methods  of  Measuring  Current  Flow  in  Pipes Ill 

Drop  in  Potential  Method 113 

Qalibration  of  Pipes 113 

Use  of  a  Direct-Current  Ratio  Relay 115 

4.  Comparing  Currents  Under  Different  Conditions 115 


CONTENTS  II 

Page 

5.  Measurement  of  Current  Flowing  from  Underground  Struc- 
tures to  Earth 115 

(a)  Differential  Current  Measurements 116 

C.  Miscellaneous  Tests. 

1.  Track  Testing 116 

(a)  Inspection 116 

(b)  Use  of  Portable  Bond  Tester '. .  117 

(c)  Autographic  Method  of  Bond  Testing 117 

(d)  Testing  of  Cross-bonds  and  Special  Work 117 

2.  Measurement  of  Leakage  Resistance  Between  Tracks  and 

Underground  Structures 119 

(a)  Importance  of  Tests  of  Roadbed  Resistance 119 

(b)  Differential  Method  of  Measuring  Roadbed  Resistance.  119 

(c)  Isolation  Method  of  Measuring  Roadbed  Resistance. . .  121 

3.  Location  and  Testing  of  High  Resistance  Joints  in  Pipes 122 

4.  Tracing  the  Source  of  Stray  Currents 123 

5.  Location  of  Unknown  Metallic  Structures  or  Connections. .  .  123 

III.  INTERPRETATION   OF   RESULT^   OF   ELECTROLYSIS 
SURVEYS 

A.  Interpretation  of  Potential  Measurements. 

1.  Maximum  Voltages  and  Track  Gradients 124 

2.  Potential  Difference  Measurements 125 

B.  Interpretation    of     Current    Measurements     on    Underground 

Structures. 

1.  Relation  of  Stray  Current  to  Corrosion 125 

2.  Relation  of  Current  to  Fires  and  Explosions 126 

C.  Interpretation    of     Measurements    of     Current    Flowing    from 

Structures  to  Earth 126 

D.  Use  of  Reduction  Factors 127 

E.  Effect  of  Reversals  of  Polarity. 

1.  Polarity  of  Pipes  Always  the  Same 128 

2 .  Polarity  of  Pipe  Changing  with  Long  Periods  of  Several  Hours.  128 

3.  Polarity  of  Pipes  Reversing  with  Periods  of  Only  a  Few 

Minutes 128 

4.  Polarity  of  Pipes  Reversing  with  Periods  of  From  Fifteen 

Minutes  to  One  Hour 129 

IV.  SELECTION  OF  INSTRUMENTS 

A.  Portable  Measuring  Instruments 129 

B.  Recording  Instruments 130 

V.  RECORDS  AND  REPORTS: 

A.  General  Discussion : . . .  131 

B.  Electric  Railways 131 

C.  Piping  Systems 132 

D.  Cable  Systems 132 

E.  Bridges  and  Buildings 132 

F.  General  Conditions 132 

VI.  TABLES...                                                                                               .  133 


12  CONTENTS 

Page 

CHAPTER  4.    European  Practice 

A.  General 134 

B.  Laws  and  Regulations. 

1.  Germany 135 

(a)   Commission  Recommendations 136 

2.  Italy 136 

3.  France 136 

4.  Spain 137 

5.  Great  Britain 137 

C.  Construction  Characteristics. 

1.  General 138 

2.  Rails 140 

3.  Rail-Bonds 141 

Table  7.     Rail  Bonding  (United  Kingdom) 143 

4.  Cross-Bonds 143 

5.  Roadbed  Construction 143 

6.  Feeders. . '. 147 

7.  Negative  Boosters 148 

Table  8.  Use  of  Negative  Boosters  (United  Kingdom) 148 

8.  Double  Trolley 149 

9.  Three-wire  System 1 49 

10.  Negative  Trolley 149 

11.  Pilot  Wires 150 

12.  Bond  Testing .  . .  150 

13.  Pipes  and  Pipe  Joints 150 

14.  Depth  of  Pipes  Below  Surface 150 

15.  Mains  on  Both  Sides  of  Streets 151 

16.  Insulating  Coverings  for  Pipes 151 

17.  Electric  Cables 151 

D.  Electrolysis  Conditions. 

1.  General 151 

2.  Voltage  and  Current  Conditions :  Experience  with  Electrolysis.  152 

(a)  Germany 152 

(b)  Italy 153 

(c)  France 153 

(d)  Great  Britain 154 

E.  Miscellaneous  Observations. 

1.  Drainage  System 155 

2.  Corrosive  Effects  of  Soil;  Earth  Resistance 155 

3.  Electrolysis  Testing  Methods 156 

4.  Economic  Aspects  of  the  Electrolysis  Problem 157 

5.  Application  to  American  Conditions , 157 

F.  Summary 158 

G.  European  Regulations  Adopted  and  Proposed. 

Germany 159 

Sec.  1.  Application  of  Rules 159 

Sec.  2.  Rail  Conductors 162 

Sec.  3.  Rail  Potential 165 

Sec.  4.  Resistance  between  Rail  and  Earth ..                       .  170 


CONTENTS  13 

Page 
G.  European  Regulations  Adopted  and  Proposed  (continued) 

Germany  (continued) 

Sec.  5.  Current  Density 172 

Sec.  6.  Control 175 

France 176 

England 177 

Spain 183 

CHAPTER  5.    Electrolysis  Research 

Further  Work  Necessary  to  Arrive  at  a  Solution  of  the  Engi- 
neering Problem. 

1.  Methods  of  Testing '. .  184 

2.  Effect  of  Different  Rail  Voltage  Drops 185 

3.  Studies  of  Electric  Railway  Power  Distribution 185 

4.  Study  of  Mitigative  Measures  Applicable  to  Affected  Struc- 

tures    185 

5.  Determination  of  Safety  Criterion  for  Pipes  Where  Positive 

to  Earth 185 

6.  Self  Corrosion 186 

7.  Fire  and  Explosion  Hazard  on  Gas  and  Oil  Pipes 186 

8.  Heating  of  Power  Cables  Due  to  Stray  Currents  on  Sheaths.  186 

Summary 187 

BIBLIOGRAPHY 

General 188 

Electrolytic  Corrosion  of  Pipes  and  Cables 188 

Surveys  and  Measurements 189 

Alternating  Current  and  Periodic  Current  Electrolysis 189 

Reinforced  Concrete 189 

Track  Construction,  Track  Leakage,  and  Rail  Bonding 189 

Insulated  Negative  Feeders 190 

Automatic  Substations 190 

Three-Wire  Operation 191 

Insulating  Pipe  Coverings 191 

Insulating  Joints 191 

Pipe  and  Cable  Drainage 191 

Legal  Aspects 192 

APPENDIX 

Tables  of  Current  Data  for  Rails  and  Pipes 193 

Sample  Data  Sheets 200 


LIST  OF  ILLUSTRATIONS 

Page 
Figure  1.  Single  Trolley  Electric  Railway  Showing  Paths  of  Return 

Current 35 

Figure  2.  Potential  Profile  of  Railway  System 36 

Figure  3.  Potential  Profile  Showing  Rails  and  Pipes  without  Connec- 
tions Between  Pipes  and  Railway  Return  Circuit 37 

Figure  4.  Effect  of  Feeding  Distance  on  Stray  Current 39 

Figure  5.  Effect  of  Feeding  Distance  on  Overall  Voltages  and  Poten- 
tial Difference  Between  Earth  and  Rails 40 

Figure  6.  Reduction  of  Track  Voltage  Drop  by  Additional  Power  Sup- 
ply Stations 41 

Figure  7.  Relation  of  Number  of  Substations  to  Annual  Charges,  for 

Interurban  Line 43 

Figure  8.  Potential   Profile   of   Two    Independent   Railway   Systems 

Showing  Effect  of  Interconnection 48 

Figure  9.  Overall  Voltage  Curves,  No  Feeders 50 

Figure  10.  Equi-Potential  Insulated  Negative  Feeder  System 50 

Figure  11.  Insulated  Negative  Feeders  Applied  to  City  Net- work  of 

Tracks 52 

Figure  12.  Graded  Insulated  Negative  Feeder  System 54 

Figure  13.  Insulated  Negative  Feeders  Applied  to  Interurban  Lines. .  .  56 

Figure  14.  Parallel  Three-Wire  System ' 58 

Figure  15.  Sectionalized  Three-Wire  System .- . . .  58 

Figure  16.  Variation  of  Coefficient  of  Corrosion  of  Iron  with  Frequency.  64 

Figure  17.  Cross-Section  of  Insulating  Joint  for  Power  Cable  Sheaths.  72 
Figure  18.  Showing  Necessity  of  Installing  Insulating  Joints  in  Services 

Connected  to  Mains  Laid  with  Insulating  Joints 75 

Figure  19.  Type  B  Bell  for  Cast  Iron  Pipe,  Designed  for  Cement  Joints .  77 
Figure  20.  Service  Pipes  Being  Damaged  Under  Car  Tracks  by  Elec- 
trolysis   80 

Figures  21  and  22.  Methods   of   Installing   Leads  for   Current   Test 

Station 112-114 

Figure  23.  Differential  Method  of  Making  Roadbed  Resistance  Meas- 
urements   118 

Figure  24.  Method  of  Making  Roadbed  Resistance  Measurements  on 

Open  Track  Construction 120 

Figure  25.  German  Tramway  Rails 139 

Figure  26.  British  Tramway  Rails 140 

Figure  27.  Rail  Weight  Data 141 

Figure  28.  Typical  Rail  Bonds — United  Kingdom 142 

Figure  29.  Cross-Bonding  Details,  etc. — United  Kingdom ."  144 

Figure  30.  Track  Construction — United  Kingdom 145 

Figure  31.  Track  Construction  and  Rails — Germany 146 

Figures  32  and  33.  Key  to  Calculation  of  Voltage  Drop  in  Rails 168 


14 


CHAPTER   1 

PRINCIPLES  AND  DEFINITIONS 
A.    ELECTROLYSIS  IN  GENERAL. 

1.  Electrolysis  is  the  process  whereby  an  electric  current  pass- 
ing from  an  electrode  to  an  electrolyte  or  vice  versa  causes  chemical 
changes  to  take  place  in  the  electrolyte.     Electrolysis  also  in- 
cludes any  chemical  changes  at  the  surface  of  an  electrode  re- 
sulting from  the  chemical  changes  in  the  electrolyte.     Electrolysis 
is  independent  of  the  heating  effect  of  the  electric  current. 

NOTE.  These  changes  usually  occur  in  a  water  solution  of 
an  acid,  alkali,  or  salt.  By  the  passage  of  an  electric  current 
through  it,  water  (containing  a  trace  of  acid)  is  decomposed 
into  hydrogen  and  oxygen,  copper  is  deposited  from  a  solution 
of  copper  sulphate,  silver  from  solutions  of  silver  salts. 
Electroplating,  electrotyping,  and  refining  of  metals  by 
electrodeposition  are  useful  applications  of  electrolysis  in 
the  arts.  Electrolysis  is  involved  in  the  charge  and  discharge 
of  storage  batteries,  and  in  the  operation  of  primary  batteries. 

In  order  that  electrolysis  may  occur,  the  following  condi- 
tions must  be  present : 

(a)  There  must  be  a  flow  of  electric  current  through  a 
conducting  liquid  from  one  terminal  to  another ; 

(b)  The  conducting  liquid  must  be  a  chemical  compound 
or  solution  which  can  be  altered  by  the  action  of  the  electric 
current. 

2.  Electrolyte,  Electrode,  Anode,  Cathode.     The  electrolyte  is 
the  solution  (or  fused  salt)  through  which  the  electric  current 
flows;  the  conducting  terminals  are  the  electrodes;  the  terminal 
by  which  the  current  enters  the  solution  is  the  anode;  the  terminal 
by  which  it  leaves  is  the  cathode. 

NOTE.  The  chemical  changes  caused  by  the  current  may 
affect  both  the  electrolyte  and  the  electrodes.  In  the  case 
of  a  solution  of  copper  sulphate  with  copper  plates  as  elec- 
trodes, copper  is  removed  from  the  anode  by  the  current 
and  carried  into  solution;  an  equal  amount  of  copper  is 
deposited  upon  the  cathode.  In  general  the  metal  travels 
with  the  current  toward  the  cathode. 

3.  Amount  of  Chemical  Action.    (Faraday's  Law.)     The  amount 
of  chemical  action  taking  place  at  the  anode  and  also  at  the  cathode 
(as  expressed  by  Faraday's  Law)  is  proportional  to  (1)  the  strength 

15 


16  PRINCIPLES  AND  DEFINITIONS 

of  current  flowing,  (2)  the  duration  of  the  current,  and  (3)  the 
chemical  equivalent  weights  of  the  substances. 

NOTE.  Otherwise  expressed,  the  quantity  of  metal  or  other 
substance  separated  is  proportional  to  the  total  quantity  of 
electricity  passing  and  the  electro-chemical  equivalent  of  the 
substance  or  substances  concerned.  The  electro-chemical 
equivalent  of  a  metal  is  proportional  to  its  atomic  weight 
divided  by  its  valence.  Faraday's  Law  is  so  exactly  realized 
in  practice  under  favorable  conditions  that  it  is  used  as  the 
basis  for  the  definition  of  the  international  ampere,  one  of  the 
fundamental  electrical  units.  (See  Passivity,  Paragraph  15.) 

4.  Cause  of  Current  Flow.     The  current  flowing  through  the 
electrolyte  may  be  due  (1)  to  an  external  electromotive  force  or 
(2)  to  the  difference  of  potential  due  to  the  use  of  electrodes  of 
different  materials  or  to  solutions  of  different  concentrations. 

NOTE.  The  first  case  is  illustrated  by  electrolysis  of 
dilute  sulphuric  acid  using  two  lead  plates  and  an  external 
battery;  the  second  by  the  electrolysis  of  the  same  solution 
using  a  zinc  and  a  copper  plate,  which  touch  each  other 
inside  or  outside  the  solution.  The  first  occurs  in  charging 
a  storage  battery;  the  second  in  the  discharging  of  a  primary 
battery  or  a  storage  battery. 

5.  Electrolysis   by   Local   Action.     Instead    of  two   plates   of 
different  metals  the  same  result  may  follow  with  one  plate  if  it  is 
chemically  impure   or  otherwise  heterogeneous,  when  immersed 
in  an  electrolyte. 

NOTE.  Such  a  plate  excites  local  currents  and  a  loss  of 
metal  occurs  at  all  the  anode  areas.  This  local  action  causes 
impure  zinc  to  dissolve  rapidly  in  a  solution  which  has  no 
action  on  pure  zinc. 

6.  Anodic  Corrosion  is  the  term  applied  to  the  loss  of  metal  by 
electrolysis  at  the  anode. 

NOTE.  When  iron  is  anode  the  iron  is  carried  into  solu- 
tion by  the  current,  the  first  product  being  a  salt  of  iron,  the 
nature  of  which  depends  upon  the  character  of  the  electrolyte. 
In  dilute  sulphuric  acid,  ferrous  sulphate  is  formed ;  in  hydro- 
chloric acid,  ferrous  chloride,  etc.  These  first  products  of 
electrolysis  are  frequently  modified  by  secondary  reactions. 

7.  Secondary  Reactions  are  the  chemical  changes  which  occui 
at  or  near  the  electrodes,  by  which  the  primary  products  of  elec- 


PRINCIPLES  AND  DEFINITIONS  17 

trolysis  are  converted   into   other  chemical  substances,  and  are 
sometimes  followed  by  other  reactions. 

NOTE.  Ferrous  hydroxide  formed  by  the  union  of  iron 
with  hydroxyl  ions  set  free  at  the  anode,  is  subsequently 
converted  into  iron  oxide  due  to  the  reactions  with  oxygen 
dissolved  in  the  electrolyte.  When  lead  is  cathode  in  an 
alkali  soil  or  solution,  the  alkali  metal  (such  as  sodium  or 
potassium)  reacts  with  water  at  the  cathode  and  forms 
alkali  hydroxide,  setting  hydrogen  free.  This  hydroxide 
may  react  with  the  lead  chemically  and  form  lead  hydroxide 
(especially  after  the  current  ceases),  which  in  turn  may  com- 
bine with  carbon  dioxide,  forming  lead  carbonate. 

8.  Calhodic   Corrosion  is  the  term  applied  to  the  corrosion 
due  to  the  secondary  reactions  of  the  cathodic  products  of  elec- 
trolysis, as  described  in  the  preceding  paragraph.     The  metal  of 
the  cathode  is  not  removed  directly  by  the  electric  current  but 
may  be  dissolved  by  a  secondary  action  of  alkali  produced  by 
the  current. 

NOTE.  The  anodic  corrosion  is  more  common  and  more 
serious;  cathodic  corrosion,  however,  sometimes  occurs  on 
lead  and  other  metals  that  are  soluble  in  alkali.  Cathodic 
corrosion  never  occurs  in  the  case  of  iron. 

B.     ELECTROLYSIS  OF  UNDERGROUND  STRUCTURES. 

9.  General.     As  used  in  this  report,  the  term  "electrolysis" 
embraces  the  entire  process  of  accelerated  corrosion  of  under- 
ground metallic  structures  due  to  stray  current.     In  the  electrol- 
ysis of  gas  arid  water  pipes,  cable  sheaths,  and  other  underground 
metallic  structures,  and  the  rails  of  electric  railways,  the  moisture 
of  the  soil  with  its  dissolved  acids,  salts,  and  alkalis  is  the  electro- 
lyte, and  the  metal  pipes,  cable  sheaths  and  rails  are  the  electrodes. 

NOTE.  Wherever  the  current  flows  away  from  the  pipes 
they  serve  as  anodes  and  the  metal  is  corroded.  Metal  or 
gas  or  alkali,  according  to  the  nature  of  the  soil,  will  be  set 
free  at  the  cathode. . 

10.  Self  Corrosion  is  the  term  applied  when  a  pipe  or  other  mass 
of  impure  or  heterogeneous  metal  buried  in  the  soil  is  corroded 
due  to  electrolysis  by  local  action. 

NOTE.  This  is  called  "self  corrosion"  because  the  electric 
current  originates  on  the  metal  itself,  without  any  external 
agency  to  cause  the  current  to  flow.  Self  corrosion  may  also 
be  due  to  direct  chemical  action. 

11.  Acceleration  of  Local  or  Self  Corrosion.     Self  corrosion  is 
accelerated  by  the  presence  in  the  soil  water  of  acid   or  salts  which 


18  PRINCIPLES  AND  DEFINITIONS 

lower  its  resistance  as  an  electrolyte,  and  also  by  cinders,  coke  or 
some  other  conducting  particles  of  different  electric  potential 
which  augment  the  local  electric  currents.  In  the  latter  case  the 
metal  need  not  be  heterogeneous. 

NOTE.  A  pipe  may  be  destroyed  in  a  relatively  short  time 
by  self  corrosion  or  local  action  if  buried  in  wet  cinders  or  in 
certain  soils. 

12.  Stray  Current  is  that  current  which  has  leaked  from  the 
return  circuit  of  an  electric  railway  system  and  flows  through  the 
earth  and  metallic  structures  embedded  therein. 

13.  Anodic  and  Self  Corrosion.     Anodic  corrosion  due  to  stray 
currents  and  self  corrosion  due  to  local  action  may  occur  simul- 
taneously, and  the  former  may  accelerate  the  latter. 

NOTE.  Hence  the  corrosion  due  to  a  given  current  plus 
the  increased  self  corrosion  induced  by  that  current  may  give 
a  greater  total  corrosion  than  called  for  by  Faraday's  Law. 
This  explains  how  the  coefficient  of  corrosion  may  exceed 
unity. 

14.  Coefficient   of   Corrosion.     The   coefficient   of  electrolytic 
corrosion  (sometimes  called  corrosion  efficiency)  is  the  quotient 
of  the  total  loss  of  metal  due  to  anodic  corrosion  (after  deducting 
the  amount  of  self  corrosion  if  any)  divided  by  the  theoretical 
loss  of  metal,  as  calculated  by  Faraday's  Law,  on  the  assumption 
that  the  corrosion  of  the  anode  is  the  only  reaction  involved. 

NOTE.  In  practice  it  is  found  that  the  coefficient  of 
corrosion  varies  widely  from  unity,  being  sometimes  as  low 
as  0.2  and  sometimes  even  above  1.5,  but  commonly  between 
0.5  and  1,1. 

15.  Passivity  is  the  name  given  to  the  phenomenon  in  which  a 
current  flows  through  an  electrolyte  without  producing  the  full 
amount  of  anodic  corrosion  which  would  occur  under  normal 
conditions. 

NOTE.  This  restricted  definition  of  passivity  has  regard 
only  to  its  effect  in  electrolysis.  Many  conditions  affect 
the  degree  of  passivity  attained,  an  initial  large  current  den- 
sity being  favorable  to  it.  Plunging  iron  into  fuming  nitric 
acid  renders  it  temporarily  passive.  A  satisfactory  explana- 
tion of  passivity  has  not  been  given. 

16.  Polarization  Voltage  (sometimes  called  polarization  poten- 
tial) is  the  temporary  change  in  the  difference  o'f  potential  "between 
an  electrode  and  the  electrolyte  in  contact  with  it  due  to  the 


PRINCIPLES  AND  DEFINITIONS  19 

passage  of  a  current  to  or  from  the  electrode.  This  change  in 
potential  difference  is  due  to  the  change  in  the  conditions  of  the 
surface  of  the  electrode  or  change  in  the  concentration  of  the 
electrolyte  (or  both),  and  under  some  conditions  is  approximately 
proportional  to  the  current  flowing,  but  in  many  cases  is  not  so 
proportional.  The  magnitude  of  the  polarization  voltage  also 
depends  on  the  material  of  the  electrode,  the  nature  of  the  electro- 
lyte, and  the  direction  of  the  current. 

17.  Alternating  or  Frequently  Reversing  Direct  Currents.     If 

alternating  currents  (or  frequently  reversing  direct  currents)  flow 
through  the  soil  between  pipes  or  other  underground  metallic 
structures,  the  metal  removed  during  the  half  cycles  when  a  pipe 
is  anode  may  be  in  part  replaced  when  it  is  cathode.  Hence,  the 
total  loss  of  metal  on  a  given  pipe  may  be  less  than  is  indicated  by 
computing  the  loss  on  the  basis  of  the  positive  part  of  the  cycle 
only,  and  in  the  case  of  alternating  current  at  commercial  fre- 
quency may  be  less  than  1%  of  such  computed  values. 

NOTE.  In  slow  reversals  of  current  the  recovery  effect  is 
less,  but  the  loss  will  be  less  than  with  direct  current  con- 
tinuously in  the  same  direction  (excepting  possibly  where 
the  phenomenon  of  passivity  may  affect  the  result). 

18.  Action  on  Underground   Metallic   Structures.     Faraday's 
Law  applies  to  electrolysis  of  metallic  structures  in  soil  as  else- 
where, the  total  chemical  action  being  proportional  to  the  average 
current  strength  and  the  time  the  current  flows  and  to  the  elec- 
trochemical equivalent  of  the  metal  of  other  substances  concerned. 
Although  local  action  and  passivity  affect  the  loss  of  metal  and 
so  apparently  modify  Faraday's  Law,  it  is  still  true  that  the 
total  chemical  action  resulting  from  the  current  flow  is  proportional 
to  the  total  current  when  local  currents  are  included. 

NOTE.  Sometimes  this  chemical  action  is  concerned  only 
with  corroding  the  anode;  sometimes  it  is  concerned  with 
breaking  up  the  electrolyte,  as  when  the  anode  is  a  noble 
metal  or  in  the  passive  state  (as  iron  and  lead  sometimes  are) : 
sometimes  both  these  effects  occur. 

The  theoretical  loss  of  iron  per  year  per  ampere  is  about 
twenty  pounds  and  of  lead  is  3.7  times  this  amount  or  about 
seventy-four  pounds.  The  loss  in  volume  of  lead  is  2.4 
to  2.6  times  that  of  iron.  The  greater  loss  in  lead  is  due  to 
the  higher  electrochemical  equivalent  of  that  metal. 

19.  Electrolysis    Mitigation.     The    two    primary    features    of 
electrolysis  mitigation  are  (1)  the  reduction  of  the  flow  of  current 


20  PRINCIPLES  AND  DEFINITIONS 

through  the  earth  and  the  metallic  structures  buried  in  the  earth, 
(2)  the  reduction  of  the  anode  areas  of  such  structures  to  a  mini- 
mum, where  the  current  is  not  substantially  eliminated  in  order 
to  reduce  the  area  of  destructive  corrosion  as  far  as  possible. 

NOTE.  The  current  in  the  underground  metallic  structures 
will  be  decreased,  other  conditions  remaining  the  same,  by 
(1)  increasing  the  conductance  of  the  return  circuit,  (2) 
increasing  the  resistance  of  the  leakage  path  to  earth,  (3) 
increasing  the  resistance  between  the  earth  and  the  under- 
ground metallic  structures,  (4)  increasing  the  resistance  of 
the  underground  metallic  structures. 

The  anode  areas  of  the  underground  metallic  structures 
will  be  decreased,  other  conditions  remaining  the  same,  by 
providing  suitably  placed  metallic  conductors  for  leading 
the  current  out  of  the  underground  structures  so  that  the 
flow  of  the  current  directly  to  the  earth  shall  be  minimized. 
This  will  change  a  portion  of  the  anode  area  to  cathode. 

20.  Electrolysis  Survey.     An  electrolysis  survey  is  the  opera- 
tion of  determining  by  means  of  proper  measurements  all  relevant 
facts  pertaining  to  electrolysis  conditions,  such  as  the  voltage 
drop  in  the  grounded  railway  return;  the  location  and  extent 
of  the  areas  in  which  the  metallic  structures  are  in  danger  from 
stray  currents;  the  condition  of  the  structures  and  adjacent  soil 
in  the  danger  areas,  and  the  extent  of  any  damage  that  may  have 
occurred;  the  seriousness  of  electrolytic  action  in  progress  and  the 
source  of  the  stray  current  producing  the  damage,  its  course  and 
magnitude  and  the  conditions  in  neighboring  structures  tending 
to  produce  electrolysis.     If  will  generally  be  found  desirable  to 
make  some  preliminary  tests  for  the  purpose  of  indicating  the 
lines  along  which  the  complete  survey  should  be  made. 

21.  Overall  Potential  Measurements.     Overall  potential  meas- 
urements are  measurements  which  are  made  to  determine  the 
difference  in  electric  potential   between   points  in  the  tracks  at 
the  feed  limits  of  the  station  and  the  point  in  the  tracks  which  is 
lowest  in  potential,  and  are  obtained  by  means  of  pressure  wires 
and  indicating  or  recording  voltmeters.     This  is  most  commonly 
applied  to  measurements  of  voltage  between  the  point  of  lowest 
potential  in  the  grounded  portion  of  a  railway  return  system  and 
the  points  of  approximately  highest   potential   on   its  various 
branches. 

22.  Potential  Gradient.    A  potential  gradient  is  the  voltage 
drop  per  unit  of  length  between  two  points  on  a  single  conductor 


PRINCIPLES  AND  DEFINITIONS  21 

or  in  the  earth,  and  is  usually  expressed  in  volts  per  thousand 
feet. 

23.  Potential    Difference.     In    electrolysis    work    the    term 
"potential  difference"  usually  means  the  difference  in  potential 
which  exists  between  nearby  points  on  separate  systems  of  con- 
ductors, or  between  conductors  and  the  earth,  e.g.,  between  pipes 
and  rails,  lead  sheaths  and  rails,  lead  sheaths  and  earth,  etc. 

24.  Arithmetical  Average.     The  arithmetical  average  value  of 
a  current  or  potential  is  the  average  value  of  all  the  instantaneous 
values  of  the  same  polarity. 

25.  Algebraic    Average.     The    algebraic    average    value    of   a 
current  or  potential  is  the  algebraic  sum  of  all  the  instantaneous 
values,  divided  by  the  number  of  such  values. 

26.  Positive   and   Negative   Areas.     Positive   areas   are   those 
areas  where  the  current  is  in  general  leaving  the  pipes  or  other 
underground  metallic  structures  for  the  earth.     Such  areas  are 
often  called  danger  areas. 

Negative  areas  are  those  areas  where  the  current  is  in  general 
flowing  to  the  pipes  or  other  underground  metallic  structures. 

NOTE.  As  the  current  often  flows  from  one  underground 
metallic  structure  to  another,  it  is  evident  that  within  a 
positive  area  there  are  local  negative  areas  and  vice  versa. 
Hence  the  terms  are  applied  somewhat  loosely,  and  according 
to  which  condition  predominates. 

Besides  the  positive  and  negative  areas  there  are  areas  of 
more  or  less  indefinite  extent  in  which  the  current  flow 
between  metallic  underground  structures  and  earth  normally 
reverses  between  positive  and  negative  values.  These  areas 
are  called  neutral  areas  or  neutral  zones. 

27.  Drainage   System.     A   drainage  system  is  one  in  which 
wires  or  cables  are  run  from  a  negative  return  circuit  of  an  electric 
railway  and  attached  to  the  underground  pipes,  cable  sheaths  or 
other  underground  metallic  structures  which   tend  to  become 
positive  to  earth,  so  as  to  conduct  current  from  such  structures 
to  the  power  station,  thereby  tending  to  reduce  the  flow  of  current 
from  such 'structures  to  earth. 

NOTE.  Three  kinds  of  drainage  systems  may  be  distinguished : 
(1)  where  direct  ties  with  wires  or  cables  are  made  between 
underground  metallic  structures  and  tracks,  (2)  where  un- 
insulated negative  feeders  are  run  from  the  negative  bus  to 
underground  metallic  structures,  (3)  where  separate  insulated 


22  PRINCIPLES  AND  DEFINITIONS 

negative  feeders  are  run  from  the  negative  bus  to  underground 
metallic  structures,  or  a  main  feeder  with  taps  to  such 
structures. 

28.  Uninsulated  Track  Feeder  System.    An  uninsulated  track 
feeder  system  is  one  in  which  the  return  feeders  are  electrically 
in  parallel  with  the  tracks.     Under  such  circumstances  the  cables 
may  be  operating  very  inefficiently  as  current  conductors  and  as 
a   means   of  reducing   track   voltage   drop,    particularly   where 
voltage  drops  in  the  grounded  portion  of  the  return  are  maintained 
at  the  low  values  usually  required  for  good  electrolysis  conditions. 
(See  Chapter  2,  Reinforcement  of  Rail  Conductivity.) 

29.  Insulated  Negative  Feeder  System.     An  insulated  negative 
feeder  system,  sometimes  called  an  insulated  return  feeder  sysem, 
or  insulated  track  feeder  system,  is  one  in  which  insulated  wires 
or  cables  are  run  from  the  insulated  negative  bus  in  a  railway 
power  station  and  attached  at  such  places  to  the  rails  of  the  track 
as  to  take  current  from  the  track  and  conduct  it  to  the   station 
in  such  a  manner  as  to  reduce  the  potential  gradients  in  the 
tracks   and   the   differences   of  potential   between   underground 
metallic  structures  and  rails,  thereby  reducing  the  flow  of  current 
in  underground  metallic  structures.     (See  Chapter  2,  Insulated 
Negative  Feeder  System.) 

NOTE.  The  insulated  negative  feeders  may  run  separately 
from  the  negative  bus  to  various  points  in  the  track  network, 
or  a  smaller  number  of  cables  may  be  used  with  suitable 
resistance  taps  made  to  tracks  at  various  places. 

With  this  system  the  drop  of  potential  in  the  track  feeders 
is  independent  of  the  drop  of  potential  in  the  tracks. 


CHAPTER   2 

DESIGN,   CONSTRUCTION,    OPERATION   AND 
MAINTENANCE 

The  practical  electrolysis  problem  is  due  to  stray  current  from 
electric  railways.  Instances  of  stray  direct  currents  from  other 
sources  sometimes  occur,  but  such  cases  are  not  specifically 
considered  in  this  report. 

Currents  straying  to  earth  from  electric  railway  tracks  frequently 
find  their  way  to  water  and  gas  pipes,  telephone  and  power  cables, 
and  other  underground  structures.  When  this  current  leaves 
these  structures  through  earth,  corrosion  results.  Thus  not  only 
are  the  structures  of  many  different  companies  subject  to  injury, 
but  by  reason  of  the  different  public  services  dependent  on  such 
structures,  the  public  as  a  whole  has  a  direct  interest  in  this  type 
of  electrical  interference.  The  problem,  therefore,  is  one  which  is 
preeminently  adapted  to  cooperative  treatment. 

In  many  cities  it  has  been  found  advantageous  to  form  joint 
committees,  composed  of  technical  representatives  of  the  several 
utilities  concerned,  to  investigate  the  local  electrolysis  situation 
and  determine  by  agreement  a  course  of  procedure  to  be  followed. 
Such  committees  should  attack  the  problem  in  an  open  and  fair- 
minded  manner  with  the  object  of  effecting,  in  the  most  economical 
way,  mitigation  of  all  the  troubles  resulting  from  the  presence 
of  stray  currents  in  the  earth,  including  corrosion,  fire  and  explo- 
sion hazards,  heating  of  power  cables,  and  operating  losses  and 
difficulties.  To  this  end,  they  should  be  composed  of  men,  or 
have  men  associated  with  them,  who  are  trained  in  the  technique 
of  electrolysis.  Active  committees  of  the  kind  described  are  now 
existent  in  Chicago,  Kansas  City,  Omaha,  St.  Paul,  New  Haven, 
Milwaukee,  and  Syracuse.  The  principle  of  cooperation  has 
been  recognized  by  the  Railroad  Commission  of  Wisconsin  in  an 
order  authorizing  an  Electrolysis  Committee  in  the  City  of  Mil- 
waukee. Such  committees  act  as  clearing  houses  of  information 
and  keep  all  the  interested  companies  informed  as  to  changes  in 
their  systems  which  may  affect  the  electrolysis  situation.  Under 
the  direction  of  such  a  committee  joint  electrolysis  surveys  may 
be  conducted  and  unified  methods  of  mitigation  installed  and 
maintained. 

The  magnitude  of  stray  currents  is  determined  by  the  design, 
construction,  maintenance,  and  operation  of  the  railway  system. 

23 


24  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

In  general,  the  same  factors  that  determine  the  amount  of  stray 
currents  are  those  that  have  a  direct  bearing  on  the  economy  of 
railway  operation.  A  good  example  is  that  of  an  insufficient 
number  of  substations,  which  results  both  in  large  stray  currents 
and  poor  railway  economy.  Similar  results  follow  from  defective 
bonding,  rails  of  inadequate  size,  or  failure  to  interconnect 
tracks.  For  this  reason,  it  is  believed  that  many  existing  railway 
systems  can  be  modified  in  such  a  way  as  to  increase  their  own 
economy  of  operation,  while  at  the  same  time  securing  important 
reduction  in  stray  current.  Measures  of  this  character,  which 
are  essential  to  the  most  economic  operation  of  the  railway,  should 
be  regarded  as  a  prerequisite  of  the  application,  either  to  the 
railway  or  to  the  affected  structures,  of  measures  specifically 
for  electrolysis  mitigation. 

Prior  to  the  consideration  of  measures  of  electrolysis  mitiga- 
tion, the  following  features  should  be  given  due  attention : 

1.  Measures  Tending  Both  to  Railway  Economy  and  the  Reduc- 
tion of  Stray  Current. 

(a)  The  return  system,   including  track  bonding,   should  be 
put  in  proper  condition. 

(b)  The  number  of  substations  should  be  made  a  maximum 
consistent  with  railway  economy. 

2.  Measures  Employed  Solely  for  Electrolysis  Prevention. 
Where  necessary  to  effect  a  still  further  reduction  in  electrolysis 

below  that  provided  by  the  most  economic  railway  system  one 
or  more  of  the  following  measures  should  be  taken : 

(a)  Applicable  to   Railways.     (1)    Additional  substations,    (2) 
Insulated  negative  feeders,  (3)  A  modified  system  of  power  dis- 
tribution such  as  a  three-wire  system. 

(b)  Applicable  to  Affected  Structures.     (1)  Insulating  joints  in 
pipes  and  cables,  (2)  Insulating  coverings  for  pipes. 

(c)  Interconnection  of  Affected  Structures  and  Railway  Return 
Circuit.     (1)  Electrical  drainage  of  cable  sheaths,   (2)  Electrical 
drainage  of  pipes. 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  -  25 

I.  RAILWAYS 

A.  FEATURES  WHICH  AFFECT  ELECTROLYSIS 
CONDITIONS 

1.  Track  Construction  and  Bonding. 

(a)  Importance  of  Rail  Circuit.     Stray  current  is  increased  by   A  [ 
insufficient   rail  weights   and   imperfectly  bonded  track  joints,     p 
While  the  major  portion  of  the  current  of  a  grounded  return 
railway  generally  returns  through  the  tracks  and  return  feeders 

to  the  power  station,  a  portion  finds  a  parallel  path  through  the 
earth  and  its  buried  metallic  structures.  As  the  current  flowing 
in  each  path  is  inversely  proportional  to  the  resistance  of  that 
path,  it  is  of  prime  importance  to  make  the  resistance  of  the  track 

circuit  as  low  as  possible  by  the  use  of  rails  of  adequate  weight . 

and  proper  bonding. 

(b)  Rail  Bond  Resistance  and  Tests.     The  contact  resistance 
of  the  bond  terminal  connection  to  the  rail  may  be  a  considerable 
part  of  the  resistance  of  the  joint  if  the  bond  is  not  properly 
installed  and  maintained  and  it  is  therefore  essential  in  selecting 
the  type  of  bond  to  be  used,  that  special  consideration  be  given 
this  feature. 

It  is  the  usual  practice  to  measure  the  resistance  of  the  bonded 
joint  including  three  feet  of  rail  in  terms  of  a  length  of  continuous 
rail.  The  equivalent  length  of  a  properly  bonded  joint  including 
three  feet  of  rail,  varies  from  3  to  6  feet,  depending  upon  the  size 
of  the  rail,  and  the  type,  length  and  cross  sectional  area  of  the 
bonds.  On  some  electrified  steam  roads  it  is  the  practice  to  bond 
so  that  the  joint  alone  will  have  an  equivalent  resistance  of  20  || 
inches  of  continuous  rail  and  to  rebond  when  this  resistance  " 
increases  to  42  inches.  On  street  railway  systems  bonding  to  an 
equivalent  length  of  3  to  6  feet  is  common  practice  where  short 
.bonds  are  used,  rebonding  when  the  joint  resistance  including 
three  feet  of  rail  increases  to  that  of  10  feet  of  rail.  A  single  No. 
0000  long  bond,  installed  around  the  splice  plates  will  have  with 
three  feet  of  rail,  a  resistance  equivalent  to  from  8  to  15  feet  of 
continuous  rail,  depending  upon  the  size  of  the  rail. 

Practice  varies  widely  as  to  the  frequency  of  testing  rail  bonds 
but  most  railway  companies  make  complete  tests  of  all  bonds  at 
least  once  each  year  and  more  frequent  tests  on  tracks  subject  to 
excessive  traffic  or  deterioration.  Good  practice  would  require 
annual  tests  of  all  bonds,  and  semi-annual  on  tracks  in  which 
the  bond  failures  exceed  five  per  cent  annually. 


26  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

(c)  Types  of  Bonds.  Bonds  may  be  classified  according  to  the 
method  of  fastening  them  to  the  rails  as  follows : 

(1)  Soldered. 

(2)  Brazed  or  Welded. 

Resistance  Weld. 
Electric  Arc  Weld. 
Oxy-Acetylene  Weld. 

(3)  Pin  Expanded. 

(4)  Compressed  Terminal. 

Solid  Single  Terminal. 
Single  or  Multiple  Stud. 

There  is  a  further  distinction  between  exposed  and  concealed 
bonds,  the  latter  being  used  where  the  prevention  of  theft  is  a 
serious  consideration,  in  which  case  the  bonds  are  installed  under- 
neath the  splice  plates. 

Local  conditions  will  largely  determine  the  type  of  bonding 
to  be  used.  Consideration  should  be  given  to  the  economy  of 
construction,  maintenance,  costs,  facilities  for  using  bonding 
equipment,  tools,  etc.  In  recent  years  there  has  been  a  marked 
tendency  toward  the  more  general  use  of  all  types  of  welded  bonds 
with  almost  complete  abandonment  of  soldered  bonds  and  those 
mechanically  applied  to  the  head  of  the  rail.  Pin-terminal  and 
compressed-terminal  bonds  are  still  extensively  used  for  applica- 
tion to  the  web  of  the  rail  but  even  here  the  welded  type  is  finding 
favor  with  many  companies.  One  reason  for  the  increasing  use 
of  oxy-acetylene  and  electric  alloy  welded  bonds  is  to  be  found 
in  the  lighter,  cheaper,  and  more  portable  tools  for  their  applica- 
tion, some  of  the  newer  methods  and  apparatus  which  have  been 
developed  for  this  class  of  work  being  far  superior  to  those  formerly 
employed. 

Soldered  Bonds  are  applied  to  the  head,  base  or  web  of  the 
rail  by  means  of  solder,  a  blow  torch  being  used  to  heat  the  rail" 
to  a  soldering  temperature.  The  difficulty  of  securing  a  permanent 
and  low  resistance  contact  has  caused  practically  all  railway 
companies  to  abandon  this  type  of  bond. 

Brazed  or  Welded  Bonds  are  applied  either  by  the  use  of  the 
heating  effect  of  an  electric  current  or  arc  or  an  oxy-acetylene 
gas  flame. 

.  The  Resistance  Weld  of  bond  to  rail  is  accomplished  by  clamping 
a  carbon  block  against  the  head  of  the  bond  and  heating  this 
block  to  a  high  temperature  by  the  passage  of  a  large  electric 
current  or  by  drawing  an  arc  on  the  face  of  the  block. 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC,  27 

In  the  Electric  Arc  process  the  arc  is  drawn  directly  on  the  rail 
and  bond  terminal.  In  both  the  resistance  and  arc  methods  of 
welding  or  brazing  the  rail  and  bond  terminals  are  brought  to  a 
welding  or  brazing  heat  and  united  in  a  solid  mass  by  filling  in 
metal,  thus  forming  a  mechanical  and  electrical  union.  The 
filling  in  metal  may  be  a  copper  or  iron  wire  used  as  an  electrode. 
When  the  bond  terminal  is  steel,  the  latter  metal  is  used.  Several 
methods,  differing  somewhat  in  the  equipment  used  and  the 
methods  of  applying  the  heat  to  the  bond  and  rail,  are  in  use,  and 
the  selection  of  the  most  suitable  of  these  will  depend  upon  a 
number  of  factors  and  often  upon  local  conditions. 

The  Oxy-Acetylene  process  is  similar  to  arc  welding  except  that 
the  heating  is  accomplished  by  means  of  an  oxy-acetylene  gas 
flame  from  a  blow  torch. 

These  methods  give  a  connection  of  low  resistance  and  short  t\ 
bonds  can  be  applied  to  the  head  of  the  rail  without  much  danger  \  \ 
of  theft  due  to   the   small  amount  of  copper  involved  and  the 
tenacious  contact  between  bond  and  rail. 

Pin  Expanded  Terminal  Bonds  have  a  hole  in  each  terminal 
through  which  a  tapered  drift  pin  is  driven  to  expand  it  into 
a  hole  drilled  in  the  web  of  the  rail  after  which  a  pin,  slightly 
larger  than  the  drift  pin,  is  driven  into  the  hole  and  left  there 
to  prevent  contraction.  This  type  of  bond  requires  great  care 
and  accuracy  in  manufacture  and  in  installation,  but  when  properly 
installed  makes  a  very  efficient  and  satisfactory  construction. 
The  essential  features  are  a  carefully  and  accurately  milled  termi- 
nal and  a  perfectly  clean,  circular-drilled  hole,  reamed  to  proper 
diameter,  in  the  rail.  Care  should  be  used  to  brighten  the  terminal 
with  emery  paper  just  before  installing  and  to  avoid  contact  with 
the  fingers  which  will  cause  corrosion  between  the  terminal  and 
the  rail.  Holes  should  be  drilled  dry  and  bonding  should  not  be 
done  except  in  fair  weather  so  there  will  be  no  moisture  to  induce 
corrosion.  This  type  of  bond  is  usually  applied  to  the  web  of  the 
rail.  As  it  requires  only  small  portable  tools  it  has  been  found 
to  be  particularly  well  adapted  to  main  line  tracks  under  operating 
conditions. 

Compressed  Terminal  Bonds  are  of  two  kinds,  one  being  a  single 
solid  terminal  bond  applied  to  the  web  of  the  rail  in  a  manner 
similar  to  the  Pin  Expanded  Terminal  bonds  described  above 
except  that  contact  with  the  rail  is  secured  by  means  of  a  heavy 
screw  or  hydraulic  compressor  applied  to  each  end  of  the  terminal, 
causing  it  to  compress  longitudinally  and  expand  laterally,  bringing 


28  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

the  copper  into  firm  contact  with  the  steel.  The  screw  compressors 
used  for  compressed  terminal  bonds  are  objectionable  where  fast 
traffic  is  maintained  on  the  tracks  as  they  clamp  over  the  head  of 
the  rail,  making  a  dangerous  condition  due  to  the  possibility  of 
causing  derailment.  The  other  is  a  single  or  multiple  stud  terminal 
bond  applied  to  the  head  of  the  rail,  the  terminal  studs  being  set 
in  holes  and  expanded  into  contact  by  hammer  blows.  This 
type  of  bond  has  been  largely  superseded  by  the  modern  types  of 
brazed- and  welded  head  bonds. 

(d)  Welded  Rail  Joints.  The  difficulties  and  uncertainties 
attending  the  proper  maintenance  of  rail  joints  and  bonds  have 
been  eliminated  to  a  large  degree  by  the  successful  use  of  several 
modern  types  of  welded  joints,  such  as  electric  resistance  and  arc 
welding,  cast  welding,  and  thermit  welding.  The  welded  joint 
in  one  form  or  another  has  been  adopted  as  a  standard  of  con- 
struction in  nearly  every  large  city  in  the  United  States.  Most 
types  of  welded  joints  have  a  conductivity  equal  to  or  greater 
than  the  continuous  rail  and  are  less  subject  to  failure  than  any 
form  of  rail  bond.  They  must  be  considered,  therefore  as  a  most 
important  factor  in  the  reduction  of  stray  current. 

Electric  Rail  Welding  is  performed  by  clamping  heavy  iron  bars 
to  the  web  of  the  rail  and  bringing  the  bars  and  the  adjacent  rail 
to  a  white  heat  by  means  of  an  electric  current.  The  process 
requires  a  heavy  and  expensive  plant  and  is  usually  carried  out  by 
contract  on  a  comparatively  large  scale.  For  this  reason  it  is  not 
well  suited  to  installations  on  small  systems.  It  is  well  adapted 
to  the  reclaiming  of  old  track  as  well  as  for  new  work  and  has 
been  applied  on  open  T-rail  construction  where  expansion  joints 
are  installed  at  intervals  to  provide  for  expansion  and  contraction. 

Arc  Welding.  There  are  several  forms  of  arc  welding  where 
the  splice  bars  are  welded  to  the  rail  at  a  number  of  points  by  the 
use  of  an  electric  arc.  Electric  arc  welding  may  be  done  under 
traffic  conditions  and  is  more  extensively  used  in  maintenance  work 
than  other  methods. 

Cast  Welding  is  accomplished  by  setting  a  mould  around  the  rail 
joint  and  pouring  molten  iron  from  a  crucible  around  the  joint. 
This  process  requires  transporting  a  portable  cupola  along  the 
street  adjacent  to  the  work.  On  account  of  the  improvement  in 
similar  types  of  joints  with  more  portable  equipment,  this  method 
is  not  now  used  as  much  as  formerly. 

The  Thermit  process  is  a  modification  of  the  cast  weld,  the  iron 
being  liberated  at  white  heat  from  a  mixture  of  iron  oxide  and 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  29 

aluminum,  which  is  ignited  in  a  crucible.  Cast  welding  is  used 
chiefly  on  new  construction  and  cannot  be  done  under  traffic. 
The  renewal  of  a  cast  weld  joint  requires  cutting  in  a  short  length 
of  new  rail  which  adds  another  joint  to  the  track. 

(e)  Cross-bonding.     The   important  objects  of  cross-bonding 
are  to  equalize  the  current  flow  between  the  rails,  thus  reducing  the 
voltage  drop  and  also  to  insure  continuity  of  the  return  circuit  in 
case  of  a  broken  length  of  rail  or  a  broken  bond  in  any  rail.     It  is 
good  practice  to  place  cross-bonds  at  intervals  of  1,000  to  2,000  feet 
on  suburban  railways  and  not  to  exceed  500  feet  on  urban  rail- 
ways.    Cross-bonding  between  parallel  tracks  is  in  some  cases 
installed  with  the  same  frequency  as  between  .the  rails  of  the 
single  track;  in  other  cases  at  less  frequent  intervals.     Some 
companies  make  a  practice  of  installing  cross-bonds  under  each 
feeder  tap  to  the  trolley  wire  or  at  every  fourth  or  fifth  span  wire, 
thus  enabling  them  to  conveniently  preserve  a  record  of  their 
locations.     In  cases  where  the  track  has  been  carefully  insulated 
cross-bonds  should  preferably  be  rubber  insulated  so  as  to  in- 
crease their  electrical  resistance  to  earth,  and  where  subject  to 
damage  from  track  tools  and  to  other  mechanical  injury  the  insu- 
lation should  be  protected  by  circular  loom  or  conduit. 

The  common  practice  of  electrified  steam  railroads  is  to  use 
cross-bonds  with  a  conductance  equal  to  one  track  rail,  or  of 
about  1,000,000  circular  mils  cross-section.  Street  and  inter- 
urban  railways  employ  bonds  having  a  cross-section  of  from  200,000 
to  500,000  circular  mils. 

(f)  Special  Track  Work  Bonding.     It  is  good  practice  to  pro- 
vide jumpers  at  switches,  frogs  and  at  other  special  track  work 
to  insure  that  the  electrical  continuity  of  the  bonded  rail  will  be 
maintained.     This  is  usually  accomplished  by  jumpers  extending 
around  the  special  work,  and  in  such  cases  the  frogs  are  bonded 
into  the  track  system,  or  where  practicable  the  special  work   is 
bonded  as  other  track  rails.     The  size  of  the  jumper  cables  to  be 
used  will  depend  upon  the  nature  of  the  traffic.     On  tracks  bearing 
heavy  traffic  a  separate  cable  is  usually  provided  for  each  rail, 
while  for  light  traffic  a  single  jumper  connecting  to  all  rails  on  both 
sides  of  the  special  work  is  sometimes  used.     In  all  cases  the 
jumpers  should  be  proportioned  to  the  current  carried  in  the 
track  and  in  no  case  less  than  a  No.  0000  for  one  track. 

In  cases  where  the  track  has  been  carefully  insulated  the  best 
practice  provides  for  the  use  of  insulated  cables  for  jumpers, 
except  in  dry  locations,  as  for  instance,  on  bridges  or  on  other 


30  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

elevated  structures  where  the  ties  are  not  in  contact  with  earth 
or  ballast.  The  electrical  leakage  from  one  bare  track  juniper  to 
damp  earth  has  been  known  to  offset  the  effect  of  many  miles  of 
most  careful  track  insulation.  Under  such  conditions,  if  positive 
to  the  earth,  the  bond  is  gradually  destroyed  by  electrolysis. 

(g)  Bonding  Tracks  with  Signal  Systems.  In  determining  the 
location  of  cross-bonds  and  jumpers  in  connection  with  alternating 
current  track  signal  circuits,  a  departure  from  ideal  spacing 
becomes  necessary,  owing  to  the  fact  that  cross-bonds  are  per- 
missible only  at  the  reactance  bonds.  The  signal  reactance 
bonds  are  located  between  the  signal  block  sections,  and  these 
sections  are  more  or  less  fixed  for  train  operating  conditions. 
The  method  used  where  tracks  carry  heavy  currents  is  to  cross- 
bond  at  all  signal  reactance  bonds  and  install  additional  cross- 
bonds  with  reactance  bonds  at  intermediate  locations  to  obtain 
the  most  satisfactory  resistance  conditions  in  the  sections  fixed 
by  the  signal  system. 

(h)  Conductivity  and  Composition  of  Rails.  The  conductivity 
of  the  track  rails  used  by  several  interurban  and  electrified  steam 
railroads  has  been  found  to  be  equivalent  to  about  Jfi  that  of 
copper,  and  this  figure  generally  holds  approximately  true  for 
girder  types  of  rails,  except  when  alloy  steel  is  used,  in  which  case 
higher  resistivities  are  found.  The  track  rails  are  specified  for 
their  mechanical  qualities,  and  where  these  interfere  with  the 
electrical  requirements,  it  is  customary  to  give  the  mechanical 
qualities  preference.  The  composition  of  rails  for  heavy  service 
used  by  one  of  the  large  electrified  steam  railroads,  in  percentage, 
is  as  follows : 

Carbon 0.62  to  0.75 

Manganese 0.70  to  1.00 

Silicon 0.10  to  0.20 

Phosphorous Not  to  exceed  0 . 04 

The  American  Railway  Engineering  Association  has  adopted 
the  following  composition  for  heavy  rails : 

Class  A  Rails  Class  B  Rails 

Carbon 0.60  to  0.75  0.70  to  0.85 

Manganese. 0.60  to  0.90  0.60  to  0.90 

Silicon Not  more  than  0.20  Not  more  than  0.20 

Phosphorous Not  more  than  0.04  Not  more  than  0.04 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  31 

2.  Track  Insulation. 

(a)  Degrees  of  Insulation.  Under  this  sub-heading  have  been 
considered,  (1)  Substantial  Insulation,  in  which  the  type  of  con- 
struction largely  prevents  the  escape  of  stray  current,  and  (2) 
Partial  Insulation,  which  comprises  using  such  means  as  are  avail- 
able to  insulate  from  the  earth  the  running  rails  of  ordinary  street 
railways  insofar  as  practicable. 

Substantial  Insulation.  Interurban  and  electrified  steam  roads 
generally  require  the  rail  to  be  supported  on  wooden  ties  set  in 
well  drained  broken  stone  or  gravel  ballast.  Such  construction 
affords  a  very  high  resistance  between  the  tracks  and  earth  and 
reduces  the  danger  of  electrolysis  to  a  minimum. 

With  10  volts  between  rail  and  ground  the  leakage  in  some 
instances  is  found  to  be  as  low  as  0.00016  amperes  per  rail  per  tie 
under  dry  weather  conditions,  increasing  to  0.0055  amperes  when 
wet.  On  double  track  with  ties  spaced  2  feet  apart  these  values 
represent  0.32  and  11.0  amperes,  respectively,  per  1,000  feet,  or  31 
and  0.91  ohms  respectively  for  1,000  feet.  On  steel  structures 
where  the  ties  are  only  partially  in  contact  with  the  ground  and 
cannot  become  waterlogged,  this  leakage  is  even  less.  The 
substantial  insulation  of  a  ballasted  roadbed  has,  in  some  installa- 
tions, been  rendered  ineffective  by  bare  negative  cables  in  damp 
earth  or  by  metallic  connections  between  the  tracks  and  steel 
supporting  structures.  Conditions  are  found  to  be  very  favorable 
for  rail  insulation  where  the  tracks  are  in  subways  or  under  cover 
protected  from  the  weather,  permitting  the  ballast  and  ties  to 
become  permanently  dry. 

Partial  Insulation.  Tracks  placed  in  city  streets  where  rails 
are  depressed  to  the  surface  of  the  ground  and  have  only  their 
upper  surface  exposed  can  be  but  partially  insulated.  The 
character  of  the  material  in  immediate  contact  with  the  rails 
has  a  large  influence  on  the  resistance  to  ground,  but  it  has  been 
repeatedly  demonstrated  that  coating  the  rails  with  an  insulating 
material  is  not  advisable,  and  the  best  plan  is  to  provide  a  roadbed, 
which,  taken  as  a  whole,  is  of  an  insulating  character.  The  use 
of  well  drained  broken  stone  or  gravel  ballast  results  not  only 
in  a  good  roadbed,  but  also  affords  a  much  higher  resistance  to 
the  escape  of  stray  current  than  does  a  roadbed  of  concrete.  It 
is  desirable  to  keep  vegetation  down  and  otherwise  keep  the 
ballast  dry  and  prevent  foreign  material  from  washing  into  it. 
Salt,  which  is  frequently  used  to  prevent  freezing  at  switches  and 


32  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

frogs,  greatly  increases  the  conductivity  of  the  roadbed  and 
thereby  facilitates  the  escape  of  stray  current. 

Electric  railways  have  experienced  some  damage  due  to  the 
corrosion  of  the  base  of  the  rail  or  of  elevated  structures  connected 
to  the  rails  in  districts  where  the  stray  current  leaves  the  structure 
for  the  earth.  Cases  are  on  record  where  this  corrosion  is  serious 
and  where  steps  have  been  taken  to  reduce  the  damage  to  elevated 
structures  by  insulating  the  rail  from  the  steel  structure.  Any 
measure  which  tends  to  insulate  the  track  from  the  soil  or  any 
mitigative  system  which  tends  to  reduce  stray  current  will  tend 
to  retard  the  electrolytic  corrosion  of  the  base  of  the  rails  and 
other  grounded  steel  structures. 

(b)  Leakage  to  be  Expected.  Under  conditions  of  substantial 
insulation  and  where  the  roadbed  is  of  open  construction  the 
leakage  varies  widely  depending  upon  the  character  of  the  ballast 
and  whether  it  is  wet  or  dry.  In  dry  weather  the  resistance  may 
be  from  10  to  15  ohms  or  even  more  per  1,000  feet  of  single  track. 
In  wet  weather  this  may  drop  to  3  to  5  ohms.  If  ties  are  treated 
with  a  3  to  1  mixture  of  gas  oil  and  creosote,  the  resistance  may  be 
double  the  above  values  whereas  with  ties  treated  with  zinc 
chloride  or  other  chemical  salts  the  resistance  may  be  one-half 
of  these  values. 

The  leakage  where  tracks  are  only  partially  insulated  will  not 
only  be  much  greater  than  where  they  are  substantially  insulated 
but  will  vary  over  a  much  wider  range.  This  is  because  the  type 
of  roadbed,  character  of  soil,  and  drainage  conditions  vary  greatly. 
It  is  known  that  well  drained  crushed  stone  ballast  with  a  Tarvia 
finish  will  have  a  resistance  from  2  ohms  to  5  ohms  per  1 ,000  feet 
of  single  track.  On  the  other  hand  the  resistance  of  roadbeds 
with  solid  concrete  ballast  in  contact  with  the  rails  and  also  earth 
roadbeds,  in  which  the  ties  are  embedded  and  therefore  in  a 
more  or  less  moist  condition,  are  much  lower  and  may  be  only 
from  0.5  to  1.5  ohms  for  1,000  feet  of  single  track. 

3.  Reinforcement  of  RaiL  Conductivity. 

Early  track  construction  practice  in  this  country  often  included 
bare  wire  laid  between  the  rails  and  connected  to  each  bond. 
Sometimes  one  such  wire  was  used  for  each  rail,  sometimes  one 
for  each  track,  and  sometimes  one  served  for  a  double  track. 
The  wires  varied  from  No.  4  to  No.  1,  and  were  either  of  copper 
or  galvanized  iron.  Their  conductivity  was  small  and  they  were 
subject  to  electrolytic  corrosion  and  mechanical  injury.  This 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  33 

construction  has  practically  gone  out  of  use.  It  is,  however, 
common  to  find  the  rails  in  the  vicinity  of  supply  stations  supple- 
mented by  large  conductors  connected  in  parallel  with  the  rails. 
This  is  not  infrequently  accomplished  by  the  use  of  bare  copper 
wire  or  cable  buried  between  rails,  and  hence  in  full  contact  with 
the  earth.  Old  rails,  bolted  and  bonded  together  and  buried 
beneath  or  beside  the  track,  have  also  been  used  in  some  cases. 
Such  buried  conductors  increase  the  leakage  from  the  tracks  and 
should  be  avoided. 

Supplementary  conductors  in  parallel  with  the  track  and 
connected  to  it  at  frequent  intervals  tend  greatly  to  insure  the 
continuity  of  the  return  circuit,  where  the  track  bonds  cannot 
be  well  maintained.  Where  copper  cables  are  so  used  the  occa- 
sional failure  of  bonds  does  not  materially  affect  the  track  drop 
and  their  use  may  be  justified  where  tracks  are  laid  on  filled  or 
spongy  ground  or  where  the  proper  maintenance  is  unusually 
difficult. 

Buried  bare  conductors,  however,  increase  the  contact  area 
between  the  return  circuit  and  the  earth,  and  the  tendency  to 
augment  stray  currents  thus  caused  offsets  to  a  greater  or  less 
extent  the  benefits  attained  by  the  reduction  of  drop. 

Copper  installed  in  this  manner  is  in  parallel  with  the  rails, 
and  therefore  has  the  same  drop  as  exists  in  the  rails.  As  track 
gradients  rarely  exceed  two  or  three  volts  per  thousand  feet, 
this  would  mean  that  the  drop  on  such  cables  would  not  exceed 
two  or  three  volts  per  thousand  feet,  which  corresponds  to  a  current 
density  of  about  190  or  280  amperes  respectively,  per  1,000,000 
circular  mils.  It  will  be  seen  that  these  densities  are  so  low  that 
such  use  of  the  copper  is  very  uneconomical  and  for  this  reason 
this  method  of  reinforcement  of  the  rail  conductivity  should  not 
ordinarily  be  used. 

Conductors  are  regarded  as  being  in  parallel  with  the  rails 
when  both  ends  are  connected  to  the  tracks  or  when  one  end  is 
connected  to  the  track  and  the  other  to  a  station  busbar  which  is 
connected  directly  to  the  rail  by  a  conductor  of  negligible  resist- 
ance. The  use  of  such  conductors  should  not  be  confused  with 
the  insulated  negative  feeder  system. 

4.  Power  Supply. 

Among  the  various  features  of  railway  construction  which  tend 
to  reduce  stray  current  none  has  made  more  rapid  advancement 
during  recent  years  than  the  development  of  multiple  feeding 


34  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

points,  principally  from  use  of  additional  substations  supplying 
the  railway  systems.  Increasing  the  number  of  .substations  will 
reduce  the  feeding  distances  and  effect  a  saving  in  distribution 
copper  and  in  line  and  return  losses,  and  will  also  reduce  the 
amount  of  current  to  be  returned  to  any  one  point.  The  general 
effect  is  to  reduce  the  track  voltage  drops,  thereby  reducing  the 
amount  of  current  which  will  stray  from  the  rails  to  subsurface 
metallic  structures. 

If     The  ordinary  street  railway  system  employs  direct  current 
(  at  from  550  to  750  volts.     Some  interurban  lines  operate  at  1200 
volts  direct  current  and  voltages  as  high  as  3000  volts  are  used 
on  the  electrified  sections  of  some  railroads. 

(a)  High  Voltage  D.  C.  Railways.     Railway  systems  of  higher 
potentials  than  the  ordinary  550-750  volt  systems  may  cause 
more  or  may  cause  less  stray  currents  than  the  latter,  depending 
upon   conditions.     With   the   same  -spacing   of  substations   the 
current  will  be  less  in  proportion  as  the  voltage  is  greater.     Usu- 
ally, however,  advantage  is  taken  of  the  higher  potential  to  locate 
the  power  supply  stations  farther  apart,  maintaining  approxi- 
mately the  same  current  density  in  the  tracks  with  the  usual 

ft  potential  gradient.     This,  of  course,  results  in  increased  overall 
jj  voltage  drops  which  tend  to  increase  the  stray  currents. 

In  making  comparison  of  high  voltage  and  low  voltage  systems 
from  an  electrolysis  standpoint,  the  difference  in  conditions  must 
be  taken  into  account.  As  a  rule  high  voltage  direct  current  is 
used  principally  on  roads  having  a  private  right-of-way  with  rails 
on  ties  supported  on  well  drained  rock  ballast.  Moreover,  the 
major  portion  of  such  lines  are  located  in  country  districts  with 
no  buried  metallic  structures  paralleling  them,  but  in  some  cases 
such  lines  pass  through  cities  or  towns,  or  at  least  enter  their 
suburbs,  in  which  event  suitable  measures  to  prevent  injury  by 
electrolysis  should  be  taken. 

(b)  Source  of  Stray  Currents.     A  single  trolley  electric  railway 
system  with  an  adjacent  buried  pipe  line  is  illustrated  in  Fig.  1, 
in  which  the  underground  network  of  pipes  is  represented  by  a 
pipe  parallel  to  the  tracks.     At  points  remote  from  the  power 
supply  station,  the  current  which  reaches  the  rails  from  the  cars 
will  divide  between  the  several  possible  paths,  and  the  amount 
flowing  along  any  path  will  be  inversely  proportional  to  the 
resistance  of  that  path.     A  portion  of  the  current,  therefore,  will 
leave  the  rails  at  points  remote  from  the  station  and  pass  through 
the  earth  to  the  adjacent  pipes,  then  flow  along  the  pipes  toward 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 


35 


K 

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V) 


36 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 


the  station,  leaving  the  pipes  near  the  station  and  returning 
through  the  earth  to  the  rails  and  thence  to  the  station  as  in- 
dicated by  the  arrows  in  Fig.  1 .  The  region  near  the  station  where 
the  pipes  are  positive  to  the  surrounding  earth,  and  where  the 
current  leaves  the  pipes  to  return  to  the  rails,  is  the  region  where 
damage  by  electrolysis  will  occur,  and  is  called  the  danger  or  posi- 
tive area. 


ial  Gradiev 


Dtsfance  End  of  Line 

Potential          Profile    of 
Rai  I  vvay    Ss  tern 

Fig.  2. 


If  the  cars  are  uniformly  distributed  along  the  line,  and  if  the 
track  is  of  uniform  resistance  throughout  its  length,  the  voltage 
profile  along  the  track  will  be  as  shown  in  Fig.  2.  This  curve  is  a 
parabola  with  a  vertical  axis  and  with  its  apex  at  the  end  of  the 
line.  The  potential  drop  from  the  end  of  the  line  to  any  point 
on  the  line  is  therefore  proportional  to  the  square  of  the  distance 
from  the  end  of  the  line.  The  slope  of  this  curve  is  a  measure 
of  the  potential  gradient.  If  the  resistance  of  the  track  is^known, 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 


37 


the  potential  gradient  at  any  point  serves  as  a  measure  of  the 
amount  of  current  flowing  in  the  rails  at  that  point. 

If  there  are  no  metallic  connections  between  the  rails  and  the 
pipes,  then  the  potential  profile  of  the  pipes  will  be  something 
like  that  indicated  in  Fig.  3. 

In  the  regions  remote  from  the  supply  station  the  pipes  are 


•ion 


Distance 


End  of  Line 


Potential    Profile   Showing     Rails   &  Pipes 
Wrfhout    Connections    Between      Pipes     and 
Railway    Return  Circuit 

Fig.  3. 

seen  to  be  negative  to  the  rails  and  near*  the  station  they  are  posi- 
tive to  the  rails.  Ordinarily  the  positive  area  extends  from  30 
to  40  per  cent  of  the  distance  from  the  supply  station  to  the  end 
of  the  line.  At  the  neutral  point  where  no  potential  difference 
exists  between  the  pipes  and  the  earth  the  stray  current  in  the 
earth  and  underground  structures  is  a  maximum. 

The  amount  of  stray  current  is  more  nearly  a  function  of  the 


38  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

overall  voltage  drop  than  of  the  potential  gradient  at  any  point. 
While  high  potential  gradients  extending  over  a  considerable 
length  of  track  will  result  in  a  high  overall  voltage  with  corres- 
pondingly large  stray  currents,  the  existence  of  a  high  gradient 
on  a  comparatively  short  section  of  track  is  of  much  less  con- 
sequence. The  reduction  of  feeding  distances  and  overall  potentials 
has  such  a  marked  influence  on  stray  currents  that  a  rather  full 
treatment  of  this  subject  is  here  given. 

(c).  Relation  of  Feeding  Distance  to  Stray  Currents  and  Overall 
Voltages.  The  effects  of  the  reduction  of  feeding  distances  on 
stray  currents  and  overall  potential  drops  are  illustrated  in  Figs. 
4  and  5.  The  stray  current  curves  are  calculated  from  the 
formulas  found  in  Technologic  Paper  No.  63  of  the  Bureau  of 
Standards,  entitled  "Leakage  Currents  from  Electric  Railways." 
They  represent  conditions  on  a  typical  line  having  the  following 
characteristics:  Double  track,  72-lb.  rails;  length  of  line,  20,000 
feet;  calculated  resistance  of  the  track,  0.004  ohm  per  1,000  feet 
(this  figure  allows  for  a  10  per  cent  increase  in  the  resistance  of 
72  Ib.  rails,  due  to  the  bonds;  it  corresponds  approximately  to 
the  resistance  of  2.5  million  circular  mils  of  copper).  The  leakage 
resistance  is  taken  as  0.4  ohm  for  1,000  feet,  of  double  track  which 
is  a  fair  average  for  city  tracks  in  paved  streets  with  a  crushed 
stone  foundation.  An  average  load  of  40  amperes  per  1,000  feet, 
corresponding  to  a  headway  of  4  minutes  each  way,  is  considered 
uniformly  distributed  along  the  line.  The  total  average  load  is, 
therefore,  800  amperes,  corresponding  to  a  station  capacity  of 
1,000  kw.,  on  the  assumption  that  the  peak  load  is  double  the 
average  load. 

Calculations  of  stray  current  have  been  made  for  both  the 
insulated  bus  and  the  grounded  bus  conditions.  This  latter  occurs 
only  when  all  of  the  stray  current  returns  to  the  negative  bus 
without  re-entering  the  track  system,  a  condition  which  does  not 
ordinarily  occur  in  practice.  An  approach  to  a  grounded  bus 
would  be  a  system  where  extensive  pipe  drainage  existed  with  a 
large  portion  of  the  current  returning  to  the  bus  from  the  under- 
ground piping  and  cable  systems.  Another  condition  which 
simulates  a  grounded  bus  is  often  found  where  bare  copper  cables 
which  are  used  to  connect  the  negative  bus  with  the  nearby  rails 
are  permitted  to  come  in  contact  with  wet  earth  or  are  laid  in  a 
stream  or  river  bed.  Railway  stations  generating  direct  current 
are  often  located  in  low  ground  or  on  rivers  where  condensing 
water  is  available  and  unless  special  precautions  are  taken  to 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 


39 


insulate  negative  cables  entering  such  stations  they  are  likely 
to  pickup  considerable  current  from  the  earth,  thereby  establishing 
the  condition  of  a  semi-grounded  bus. 


Fig.  4  shows  the  total  current  returning  to  a  single  supply  station 
located  at  the  end  of  the  line.  The  stray  current  at  any  point  is 
also  shown  for  the  cases  of  the  bus  grounded  and  the  bus  not 
grounded.  By  insulating  the  bus  the  maximum  value  of  the  stray 


40 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 


current  is  reduced  from  417  amperes  to  147  amperes  and  by  putting 
the  supply  station  at  the  middle  of  the  line  instead  of  at  the  end 
and  thereby  reducing  the  feeding  distance  to  one-half,  the  maximum 


value  of  the  stray  current  with  insulated  bus  is  reduced  from  147 
amperes  to  about  24  amperes. 

Fig.  5  shows  the  overall  voltage  curves  for  the  same  line  fed 
from  the  end,  from  the  center,  and  also  from  two  stations  located 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 


41 


at  one-fourth  and  three-fourths  of  the  distance  to  the  end  of  the 
line  respectively.  Shortening  the  feeding  distance  to  one-half 
reduces  the  overall  voltage  to  one-fourth  of  the  original  value  and 
cutting  the  feeding  distance  to  one-fourth  reduces  the  overall 
voltage  to  one-sixteenth  of  the  original  value;  or  as  previously 


stated,  the  overall  voltage  varies  as  the  square  of  the 
feeding  distance.  The  curves  in  Fig.  5  are  based  on  theoretical 
conditions  with  no  stray  current.  The  actual  overall  voltages 
would  be  somewhat  less  because  of  part  of  the  current  being  in  the 
earth.  The  dotted  lines  in  Fig.  5  illustrate  in  a  'general  way  the 


42  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

potential  of  the  earth  and  pipes  under  the  several  conditions  of 
feeding  and  the  shaded  portions  represent  the  areas  where  the 
earth  and  pipes  are  positive  to  the  rails 

The  effect  of  providing  additional  centers  of  power  supply 
can  also  be  illustrated  by  the  curves  in  Fig  6,  which,  while  cal- 
culated on  the  assumption  of  no  stray  current,  illustrate  in  a 
simple  case,  the  effects  which  have  been  observed  in  practice. 

The  curve  SAO  represents  the  track  voltage  drop  on  a  portion 
of  an  electric  railway  system  having  a  uniformly  distributed  load. 
The  curve  SBF  illustrates  the  condition  of  a  substation  located 
at  P,  33  per  cent  of  the  distance  from  Q  to  S,  carrying  20  per  cent 
of  the  total  load.  In  this  curve  the  portion  BF  is  identical  with 
AO.  As  the  load  is  uniformly  distributed,  33  per  cent  of  the  load 
is  on  the  portion  of  the  line  shown  by  PQ,  and  of  this  33  per  cent, 
20  per  cent  is  carried  by  the  substation  P.  The  remainder,  or 
13  per  cent,  is  carried  by  the  station  S.  The  point  B  on  the  curve 
SBF,  therefore,  corresponds  to  the  point  N  on  the  curve  SAO, 
the  distance  QR  being  13  per  cent  of  QS. 

In  the  same  manner  the  curves  SCG,  SDH,  and  SEK  are  drawn 
showing  the  conditions  when  the  station  P  carries  40  per  cent,  60 
per  cent,  and  80  per  cent,  respectively,  of  the  total  load.  The 
summit  of  the  curve  SMD,  in  which  the  station  P  carries  60  per 
cent  of  the  load,  is  located  so  that  PL  equals  60  per  cent  minus 
33  per  cent,  or  27  per  cent  of  the  total  length  SQ  to  the  left  of  P. 
The  distance  QL  is,  therefore,  60  per  cent  of  the  total  length  QS. 

In  general,  the  conditions  are  more  complicated  than  those 
here  assumed,  and  will  ordinarily  prevent  an  accurate  determina- 
tion of  the  relative  potentials  of  the  negative  buses  of  the  two 
stations. 

(d)  Economic  Considerations  Invoked  in  Additional  Supply 
Stations.  The  practical  limit  of  feeding  distances  is  one  that 
cannot  be  determined  by  any  general  formula  designed  to  fit  all 
conditions.  The  economic  aspects  of  the  problem  are  far  more 
complex  than  they  appear  at  first  glance  and  the  proper  solution 
involves  a  careful  study  of  local  conditions.  However,  an  increase 
in  the  number  of  power  supply  stations  may  be  said  generally  to 
reduce  stray  currents  to  a  marked  degree  and  with  the  advent  of 
automatic  control  for  railway  substations  the  increase  in  the 
number  of  feeding  points  economically  obtainable  by  this  means 
should  result  in  greatly  improved  electrolysis  conditions. 

The  number  of  substations  for  a  given  set  of  conditions  may 
often  be  materially  increased  by  some  additional  capital  expendi- 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 


43 


ture,  but  with  no  increase  in  annual  charges.  Also,  the  original 
equipment  may  be  distributed  to  additional  stations  with  little 
or  no  capital  expenditure,  due  to  saving  of  feeder  copper,  and 
with  no  increase  in  annual  charges. 


Number  of  Substations 


Relation  of  Number    of  5ubsfa4ions  -fo   Annual 
Cnaraes  -for    Interurban     Line 

Fig.  7. 

The  curves  in  Fig.  7  show  the  results  of  calculations  on  a  typical 
interurban  railway  system.  They  are  based  on  the  data  con- 
tained in  the  paper  by  H.  F.  Parshall  presented  to  the  (British) 


44  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

Institute  of  Civil  Engineers,  Volume  199;  and  on  present  day 
prices  of  copper  and  electrical  machinery  and  labor. 

Ordinarily  in  laying  out  the  number  of  substations  for  a  given 
electric  railway  system,  the  minimum  number  consistent  with 
economy  will  be  the  number  selected,  such  as  represented  by  the 
curve  for  manual  operation  at  A.  With  the  growth  of  traffic 
the  number  of  stations  in  operation  becomes  increasingly  inade- 
quate until  a  condition  is  reached  represented  by  the  point  B  on 
the  curve,  when  additional  substations  are  again  added.  In 
other  words  it  is  customary  to  operate  along  the  curve  from  A  to 
B  with  an  insufficient  number  of  substations.  It  appears,  how- 
ever, that  by  operating  between  C  and  A  on  the  curve  instead  of 
between  A  to  B  an  increase  of  about  40  per  cent  in  the  number  of 
substations  can  be  made  without  effect  on  the  total  annual  charges. 

It  has  been  shown  on  page  40  of  this  report  that  when  the 
overall  voltage  is  divided  by  4  the  amount  of  stray  current  will 
be  about  one-sixth  for  the  particular  conditions  discussed.  An 
increase  of  40  per  cent  in  the  number  of  substations  will  decrease 
the  overall  voltage  to  about  one-half  of  the  former  value  and  there- 
fore reduce  the  stray  current  to  about  one-third.  It  appears, 
therefore,  that  by  selecting  the  maximum  number  of  substations 
consistent  with  economy  instead  of  the  minimum  number,  the 
railway  companies  could  reduce  to  a  large  extent  the  stray  currents 
without  appreciably  affecting  their  total  annual  charges  and  this 
method  should  be  considered  as  one  of  the  best  possible  solutions 
of  the  electrolysis  problem.  The  curve  for  automatic  substations 
is  even  flatter  than  that  for  manually  operated  stations,  indicating 
that  a  very  large  increase  in  the  number  of  automatic  stations 
beyond  the  point  of  maximum  economy  may  be  employed  without 
materially  increasing  the  annual  charge. 

It  appears  from  these  curves  that  if,  while  the  electric  railway 
companies  are  increasing  their  power  supply,  they  will  at  the  same 
time  increase  the  number  of  power  supply  stations  to  the  maximum 
economical  number,  then  they  can  without  any  increase  in  the 
total  annual  charges  eliminate  the  greater  portion  of  the  stray 
currents  which  cause  electrolysis. 

In  many  situations  the  combination  of  railway  substations  with 
light  and  power  substations  may  offer  additional  opportunities 
for  economically  providing  points  of  supply  without  additional 
expense  for  buildings  and  attendance. 

(e)  Automatic  Substations.  During  recent  years  considerable 
progress  has  been  made  in  the  development  of  automatic,  semi- 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC,  45 

automatic,  and  remote  control  substations  for  electric  railway 
service. 

Automatic  stations  were  first  used  on  interurban  lines  having 
infrequent  service  and  the  installation  usually  consisted  of  a  300 
or  500  kw.  machine.  When  a  car  or  train  of  cars  approaches  one 
of  these  interurban  substations  the  voltage  of  the  trolley  falls 
and  when  it  has  reached  a  certain  point  the  substation  auto- 
matically starts  up  and  carries  the  load  while  the  train  is  in  its 
vicinity.  As  the  car  recedes  from  the  substation  the  demand  for 
current  decreases  and  when  the  load  has  reached  a  predetermined 
minimum  the  substation  shuts  down. 

This  type  of  substation  with  small  converters  has  been  success- 
fully introduced  in  some  cities,  the  most  notable  installation  being 
that  at  Des  Moines,  Iowa,  where  six  substations  were  distributed 
throughout  the  city  to  replace  one  centrally  located  power  supply 
station. 

The  characteristics  of  large  city  loads  are  different  from  those 
on  interurban  lines.  The  movement  of  a  single  car  produces  but 
slight  fall  in  the  trolley  potential  and  the  starting  and  stopping 
of  the  substation  is  governed  by  the  demand  for  power  during  the 
morning  and  evening  rush  hours.  A  few  substations  with  large 
converters  have  been  provided  for  such  city  service  and  are  now 
in  experimental  operation.  Remote  control  substations  are  also 
being  developed  for  city  service  where  they  are  required  to  operate 
continuously  throughout  the  load  period  of  the  day  or  during  the 
morning  and  evening  peaks. 

Semi-automatic  equipment,  consisting  of  re-closing  circuit 
breakers,  time  switches,  and  protective  devices  have  been  installed 
in  a  number  of  railway  substations  at  a  very  much  smaller  cost 
than  would  be  required  for  full  automatic  operation.  The  circuit 
breakers  in  the  positive  feeders  automatically  re-close  after  a 
definite  time  interval  provided  the  short  circuit  or  overload  has 
been  removed.  The  synchronous  converter  has  to  be  started  by 
hand  and  may  be  shut  down  either  by  a  time  switch  or  by  hand. 
Otherwise  it  operates  in  a  manner  similar  to  those  provided  with 
full  automatic  control. 

The  first  cost  of  automatic  substations  is  often  justified  by  the 
saving  in  operating  labor  an_d  feeder  losses  and  the  recovery  of 
existing  feeding  copper.  Minor  savings  arise  from  the  elimination 
of  light  load  losses  and  the  station  heating.  A  further  benefit  also 
to  be  derived  from  their  general  use  is  better  voltage  conditions 
and  therefore  faster  car  schedules. 


46  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

The  total  amount  of  substation  equipment  now  operated  auto- 
matically is  in  excess  of  50,000  kw.,  and  much  of  the  equipment 
being  installed  is  intended  for  automatic  operation  or  remote 
control.  The  increased  savings  attending  this  development  will 
undoubtedly  increase  the  number  of  substations  which  can 
economically  be  installed  on  both  interurban  and  city  systems, 
and  if  full  advantage  is  taken  of  these  economics,  the  feeding 
distances  will  be  reduced  to  such  an  extent  as  to  greatly  reduce 
stray  currents  generally. 

( f )  Location  of  Supply  Stations.     As  pipes  and  other  under- 
ground structures  become  increasingly  positive  to  the  earth  as 
they  approach  street  railway  supply  stations  or  the  low  potential 
points  on  the  track  system,  it  is  obvious  that  if  stations  were 
located  away  from  pipe  networks  trouble  from  electrolysis  would 
seldom  occur.     As  a  rule  other  considerations  will   determine 
the  location  of  supply  stations  in  cities.     However,  on  interurban 
lines  the  protection  of  piping  systems  in  small  towns  against 
electrolytic  corrosion  often  presents  a  grave  problem  because  of 
the  long  feeding  distances  and  the  difficulty  of  employing  the 
measures  of  mitigation  ordinarily  used  in  city  systems.     Under 
such  conditions  the  location  of  the  supply  station  at  a  distance 
from  the  city  and  away  from  the  underground  structures  may  be 
the  most  satisfactory  way  of  insuring  their  protection.     This  is 
particularly   true    of   automatic   substations   which   require   no 
regular  attendants. 

The  character  of  the  earth  in  the  vicinity  of  supply  stations 
naturally  has  an  important  effect  on  the  magnitude  of  stray 
currents.  It  is,  therefore,  desirable  to  avoid  connecting  negative 
feeders  to  tracks  in  unusually  wet  locations. 

(g)  Alternating  Current  Systems.    When  the  first  alternating 
current  railways  were  proposed,  the  question  of  possible  electrolytic 
effects   received   special   investigation.     Considerable   work  was 
done  upon  a  laboratory  scale,  in  which  it  was  established  that 
alternating  currents  could  produce  corrosion  on  electrodes  of  the 
metals  commonly  used  underground,  such  as  lead  and  iron,  but 
that  the  effects  were  very  much  less  in  magnitude  than  those 
produced  by  equivalent  direct  currents,  usually  less  than  one  per 
cent  and  in  most  cases  negligible.     See  Fig.  16. 

The  objections  to  the  substitution  of  alternating  current  for 
direct  current  in  the  case  of  systems  already  installed  in  large 
cities  are  so  well  known  and  so  serious  that  the  question  needs  no 
discussion. 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  47 

5.  Interconnection  of  Tracks. 

Electrical  interconnection  between  parallel  tracks  in  close 
proximity,  or  of  tracks,  one  of  which  passes  over  the  other,  be- 
longing to  the  same  or  different  railway  systems  is  usually  a 
necessity  in  order  to  prevent  wide  fluctuations  of  voltage  between 
the  tracks.  Such  interconnections  tend  to  equalize  the  potentials 
of  the  tracks  so  connected  and  thus  tend  to  prevent  the  flow  of 
current  from  the  track  of  high  potential  through  earth  and  inter- 
vening metallic  subsurface  structures  to  the  track  of  low  potential. 
In  general  such  interconnections  also  afford  a  saving  in  track  losses. 

Whether  parallel  tracks  should  be  connected  naturally  depends 
upon  the  distance  between  tracks,  location  of  supply  stations, 
leakage  characteristics  of  the  roadbeds  and  other  local  con- 
siderations. 

Interconnection  generally  reduces  the  track  voltage  drop  by 
providing  more  metallic  paths  for  the  current.  It  has  also  the 
same  general  effect  as  cross-bonding  between  rails  of  the  same 
tracks,  in  that  if  one  track  circuit  should  be  accidentally  opened 
the  current  would  be  shunted  around  through  the  interconnection 
to  the  other  track.  As  a  rule  interconnection  of  tracks  will 
improve  electrolysis  conditions  but  may  be  detrimental  to  one 
locality  while  improving  conditions  in  another.  A  failure  of  one 
of  the  companies  to  maintain  its  bonding  would  naturally  tend  to 
increase  the  current  on  the  better  bonded  track. 

Interconnection  of  tracks  has  been  found  to  be  particularly 
advantageous  where  two  or  more  lines  of  electric  railways  operating 
in  one  locality  and  belonging  to  the  same  or  to  different  systems 
are  supplied  from  two  or  more  power  stations  located  in  different 
parts  of  the  city.  By  interconnecting  the  tracks  of  such  lines  in 
the  neighborhood  of  the  power  stations  and  also  at  several  inter- 
mediate points  a  reduction  in  the  resistance  of  the  return  circuit 
can  be  brought  about  whereby  the  drop  formerly  existing  in  one 
track  can  be  balanced  by  the  drop  in  the  opposite  direction  in  the 
other  track.  The  rail  drop  in  each  track  is  greatly  reduced  and 
all  high  potential  gradients  between  tracks  eliminated. 

Where  the  tracks  of  the  two  independent  railway  systems  are 
parallel  and  a  short  distance  apart,  and  fed  by  power  supply 
stations  in  opposite  directions  the  potential  profiles  of  the  rails 
will  be  as  shown  in  Fig.  8  in  which,  for  simplicity,  the  negative 
buses  at  the  two  stations  have  been  assumed  to  be  at  the  same 
potential.  In  the  figure  are  also  indicated  the  potential  profiles 
of  the  pipes  adjacent  and  parallel  to  the  two  sets  of  tracks. 


48 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 


If  then  gas  or  water  pipes  extending  from  the  parallel  mains 
cross  under  two  sets  of  tracks  at  different  locations  where  the 
tracks  are  at  a  considerable  difference  of  potential,  as  at  RB,  Fig. 
8,  then  the  pipes  may  be  negative  to  one  track  and  positive  to  the 


Station  A 


Station  B 


Potential  Profile 

oftwo        Independent     Railway    Systems 
Sho  wincr    Effect       of    Interconnection 

Fig.  8. 

other.     At  the  crossings  where  the  pipes  are  positive  to  the  tracks 
electrolysis  will  be  liable  to  occur. 

If  now  the  rails  of  the  two  systems  are  interconnected  at  points 
near  the  two  stations  and  also  at  intermediate  points  the  potential 
profile  along  the  rails  after  such  interconnection  will  be  as  shown 
by  the  curve  OYP.  It  will  be  noted  that  this  interconnection 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  49 

results  in  a  very  considerable  reduction  of  the  potential  drop  in 
the  return  circuit,  and  the  resulting  reduction  in  the  losses  will 
in  many  cases  be  alone  sufficient  to  warrant  the  cost  of  the  inter- 
connections. 

Railway  systems  employing  track  circuit  signals  must  insulate 
their  rails  used  for  signal  circuits  from  other  systems  in  order  that 
other  currents  may  not  be  introduced  in  the  signal  circuits  and 
for  this  reason  cannot  avail  themselves  of  the  advantages  of  inter- 
connection. This  applies  only  to  rails  used  for  signal  circuits. 

B.    FEATURES  OF  RAILWAY  CONSTRUCTION  AND 

OPERATION  EMPLOYED  FOR  ELECTROLYSIS 

MITIGATION 

1.  Insulated  Negative  Feeder  System. 

Of  the  various  methods  of  railway  construction  and  operation 
employed  to  improve  electrolysis  conditions,  the  insulated  nega- 
tive feeder  system  has  been  most  widely  used.  While  it  has  been 
generally  thought  that  such  a  system  is  necessary  in  connection 
with  a  large  supply  station  if  underground  structures  are  to  re- 
ceive adequate  protection,  the  present  tendency  to  greatly  increase 
the  number  of  railway  supply  stations,  and  particularly  the 
development  of  the  automatic  substation  makes  the  extensive 
use  of  insulated  negative  feeders  less  important.  An  increase  in 
the  number  of  track  drainage  points  is  often  more  economically 
attained  by  the  use  of  more  substations  than  by  the  use  of  insulated 
negative  feeders.  The  tendency  is  now  in  the  direction  of  a 
relatively  few  short  insulated  negative  feeders  and  a  large  num- 
ber of  substations,  rather  than  an  extensive  use  of  insulated  feeders 
from  a  few  large  supply  stations. 

(a)  Description.  In  the  insulated  negative  feeder  system, 
instead  of  tying  the  tracks  directly  to  the  negative  bus  and  de- 
pending on  the  tracks  and  such  copper  conductors  as  may  be  in 
parallel  with  them  to  return  the  current  to  the  supply  station,  the 
connection  at  the  station  is  either  removed  or  a  suitable  resistance 
is  inserted  and  insulated  feeders  are  run  from  the  bus  to  various 
points  on  the  track.  By  thus  taking  the  current  from  the  rails 
at  numerous  points,  high  current  densities,  and  consequently 
high  gradients  and  overall  voltages,  can  be  avoided  to  any  desired 
degree.  As  the  feeders  are  entirely  insulated  from  the  earth 
except  at  points  of  connection  to  the  tracks,  the  actual  drop  in 
potential  in  the  different  feeders  is  of  no  importance  so  far  as 
electrolysis  is  concerned,  so  long  as  the  drop  is  approximately 


50 


DESIGN,  CONSTRUCTION,  OPERATION,  HTC. 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  51 

the  same  in  all  feeders.  It  is  possible,  therefore,  to  impose  any 
limiting  value  of  overall-track  drops  and  track  potential  gradients 
on  the  track  and  still  be  free  to  design  the  feeders  to  give  maximum 
economy  which  is  not  possible  when  the  feeders  are  connected  in 
parallel  with  the  track. 

Insulated  feeders  are  sometimes  designed  for  equal  potential 
drops,  in  which  case  the  several  points  of  connection  to  the  tracks 
are  at  the  same  potential  and  the  system  is  called  an  equi-potential 
or  balanced  system.  When  the  shorter  feeders  are  designed  for  a 
lower  drop  than  the  longer  feeders,  the  system  is  called  a  graded 
potential  system. 

Fig.  9  shows  the  overall  voltage  curves  representing  conditions 
on  a  track  which  is  connected  directly  to  the  negative  bus  and 
with  which  no  additional  feeders  are  employed.  The  curves  are 
parabolas  with  the  same  constants  as  those  in  Figs.  2  and  5.  Fig. 
10  illustrates  the  same  system  with  insulated  negative  feeders 
extended  to  four  points  on  the  track,  two  in  each  direction,  with 
a  resistor  connected  to  the  nearest  point  on  the  track.  The 
feeders  and  resistance  are  so  proportioned  that  the  drop  on  all  is 
the  same  under  average  load  conditions  and  they,  therefore,  form 
an  equi-potential  system.  The  curved  lines  represent  the  poten- 
tial of  the  track  from  point  to  point,  and,  as  in  Fig.  9,  the  curves 
are  arcs  of  parabolas. 

An  equi-potential  system  of  this  kind,  while  it  reduces  potential 
differences  on  the  tracks  to  a  minimum  and  therefore  affords  the 
maximum  reduction  of  stray  current,  usually  involves  increased 
energy  losses  in  the  return  circuit  as  the  rails  are  merely  used 
as  distributing  mains  for  the  feeders  and  are  not  taken  advantage 
of  to  return  current  to  the  supply  station.  The  equi-potential 
principle  is  better  adapted  to  a  city  network  than  to  a  single  line, 
as  feeders  can  be  extended  to  several  points  on  the  network  at 
approximately  the  same  distance  from  the  station,  and  these 
points  can  thus  be  maintained  at  the  same  potential.  As  a  rule, 
however,  a  gradient  is  permitted  between  the  points  so  selected 
and  the  track  at  its  nearest  approach  to  the  supply  station.  An 
arrangement  approaching  an  equi-potential  system  is  shown  in 
Fig.  1 1 ,  where  four  feeders  are  connected  to  the  track  at  important 
intersections  and  connection  made  to  the  track  near  the  station 
through  a  resistance.  One  of  the  feeders  is  shown  connected  to^ 
the  track  at  two  points,  a  resistance  being  inserted  at  the  point 
nearest  the  station. 

This  system  and  also  the  one  illustrated  in  Fig.  10  are  practically 


52 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  53 

equivalent,  in  the  reduction  of  stray  currents,  to  independent 
substations  at  the  several  points  where  the  current  is  removed 
from  the  track;  that  is,  the  results,  so  far  as  voltage  drop  on  the 
tracks  is  concerned,  is  the  same  whether  a  number  of  stations  or 
an  equal  number  of  insulated  negative  feeders  be  employed,  but 
the  energy  losses  in  both  the  positive  and  negative  conductors  are 
very  much  greater  with  the  negative  feeder  system  than  with  the 
same  number  of  substations. 

Fig.  12  illustrates  an  insulated  negative  feeder  system  so  de- 
signed that  the  direction  of  the  current  in  the  rails  is  not  reversed 
as  in  the  equi-potential  system.  This  graded  potential  system 
results  in  a  slightly  higher  potential  at  the  terminal  of  each  suc- 
ceeding feeder,  starting  from  the  station,  and  these  higher  poten- 
tials on  the  longer  feeders  result  in  higher  overall  track  potentials 
than  with  the  equi-potential  system,  but  allow  a  material  saving 
in  copper  in  the  negative  conductors. 

In  designing  graded  potential  feeder  systems,  it  is  customary  to 
limit  the  gradients  on  the  tracks  to  some  definite  amount,  such, 
for  example,  as  an  average  value  of  0.5  volt  per  1000  feet  and  to 
remove  all  of  the  current  from  the  track  over  an  insulated  feeder 
wherever  this  limiting  gradient  is  reached.  By  removing  no  more 
current  at  any  point  than  has  accumulated  up  to  that  point,  the 
current  in  the  track  is  nowhere  reversed  and  a  continuous  gradient 
toward  the  station  is  maintained  as  illustrated  in  Fig.  12. 

(b)  Application  of  Insulated  Negative  Feeders.  No  definite 
rules  can  be  laid  down  regarding  when  and  to  what  extent  insu- 
lated negative  feeders  should  be  used.  In  city  networks  the 
negative  bus  should  generally  be  connected  to  the  track  at  more 
than  one  point,  that  is,  negative  feeders  should  be  extended  along 
the  tracks  to  nearby  intersections.  Small  stations  of  300  to  500 
k.w.  capacity  in  city  networks  may  usually  be  connected  directly 
to  the  track  at  one  point  only  and  preferably  to  the  nearest  track 
intersection. 

Insulated  negative  feeders  should  be  run  from  the  negative  bus 
to  the  rails  in  such  a  manner  as  to  insulate  them  thoroughly  from 
the  earth  and  from  each  other.  The  tying  together  of  any  of  these 
feeders  should  be  avoided.  In  some  cases,  however,  it  may  be 
allowable  to  tie  a  single  feeder  to  the  rail  at  two  or  more  points 
through  resistances  to  adjust  the  currents  drawn  from  the  tracks 
at  the  various  points  of  connection. 

Connections  to  tracks  in  wet  locations  make  possible  excessive 


54 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 


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DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  55 

current^discharge  from  adjacent  underground  structures  and 
should  therefore  be  avoided  where  possible. 

Means  should  be  provided  on  all  negative  feeders  and  feeder 
taps  for  conveniently  measuring  the  current  flow  thereon,  and 
where  practicable  these  means  should  be  installed  within  the 
railway  power  station. 

Application  to  Interurban  Lines.  In  the  case  of  a  single  line, 
little  is  to  be  gained  by  the  use  of  insulated  negative  feeders  unless 
they  are  run  considerable  distances  from  the  power  supply  station. 
For  this  reason  they  are  not  as  well  adapted  to  reducing  stray 
currents  from  interurban  lines  as  from  city  networks  as  the  follow- 
ing explanation  will  show. 

It  has  been  shown  in  the  section  on  Power  Supply  that  stray 
current  results  from  the  action  of  large  overall  voltages  rather 
than  from  high  potential  gradients.  Large  overall  voltages  may 
be  produced  either  by  concentrated  city  loads  over  relatively 
short  feeding  distances  or  by  comparatively  light  loads  on  long 
lines.  The  former  condition  can  often  be  effectively  dealt  with 
by  the  use  of  insulated  feeders  because  of  the  short  distances  in- 
volved and  a  traffic  of  sufficient  density  to  justify  such  an  ex- 
penditure. A  very  different  condition  exists  on  interurban  lines 
where  a  corresponding  reduction  in  overall  voltages  would  require 
very  long  insulated  feeders  entailing  large  expenditures  for  copper 
and  large  power  losses. 

The  effect  of  installing  insulated  negative  feeders  within  the 
limits  of  a  small  town  through  which  an  interurban  lines  passes 
is  illustrated  in  Fig.  13.  Without  the  use  of  negative  feeders,  that 
part  of  the  piping  system  within  the  city  limits  is  shown  to  be 
positive  to  the  tracks,  a  condition  which  is  often  found  in  practice, 
although  not  a  reliable  criterion  as  to  the  degree  of  hazard  to 
underground  structures  as  pipes  are  sometimes  positive  to  the 
rails  and  negative  to  the  adjacent  earth.  If  the  potential  gradients 
on  the  tracks  within  the  city  are  reduced  or  eliminated  by  the  use 
of  insulated  feeders,  the  overall  voltages  are  only  slightly  affected 
and  the  potential  difference  between  the  pipes  and  tracks  not 
greatly  reduced.  In  some  instances  where  insulated  feeders  have 
been  applied  on  interurban  lines,  the  positive  area  has  actually 
been  extended  and  no  material  improvement  in  the  general 
condition  effected. 

It  is  not  the  intention  here  to  condemn  entirely  the  use  of  insu- 
lated^negative  feeders  for  interurban  electric  lines,  because  in 
some  cases  they  have  been  successfully  used.  Local  conditions 


56 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  57 

vary  widely  and  each  problem  should,  therefore,  be  worked  out  on 
its  own  merits.  However,  it  can  safely  be  said  that  this  method 
of  electrolysis  mitigation  is  not  so  well  adapted  to  interurban 
lines  as  to  city  systems. 

(c)  Negative  Boosters.  Negative  boosters  are  sometimes  used 
in  connection  with  the  insulated  negative  feeder  system  abroad, 
but  not  in  this  country,  so  far  as  known.  Unusually  long  feeders 
which  would  have  to  be  very  heavy  in  order  to  keep  the  voltage 
drop  comparable  with  that  on  the  other  feeders  can  be  reduced  to 
the  minimum  size  that  will  carry  the  current  if  provided  with  a 
booster.  When  so  used,  the  booster  permits  a  saving  in  copper 
but  involves  an  additional  energy  loss  on  the  conductor.  Boosters 
can  also  be  used  to  equalize  the  voltage  drops  on  feeders  of  differ- 
ent lengths.  They  have  proved  economical  under  certain  condi- 
tions and  uneconomical  under  others.  In  general  it  is  simply  a 
question  of  the  fixed  charges  on  copper  as  against  the  fixed  charges 
and  operating  cost  of  machines. 

2.  Three-Wire  System. 

(a)  Description.  This  method  of  power  distribution  is  similar 
to  that  commonly  used  for  city  light  and  power,  and  known  as  the 
Edison  three- wire  system.  It  may  take  two  different  forms  which 
are  the  same  in  principle,  but  which  differ  radically  in  the  arrange- 
ment of  the  feeder  system.  One  of  these,  known  as  the  parallel 
three- wire  system,  is  directly  analogous  to  the  ordinary  three-wire 
power  and  lighting  system.  The  typical  arrangement  for  the  case 
of  a  double-track  line  using  this  system  is  shown  in  Fig.  14.  Here 
one  trolley  is  negative  and  the  other  positive,  the  tracks  being 
the  neutral  conductor.  This  results  in  a  potential  difference  be- 
tween trolley  wires  equal  to  twice  the  operating  voltage  at  points 
of  connection  between  the  trolley  sections.  It  is  evident  that 
only  the  difference  in  the  load  on  the  two  sides  of  the  line  returns 
to  the  powerhouse  on  the  track,  although  there  may  at  times  be 
heavy  circulating  currents  flowing  between  cars  in  short  sections 
of  track.  If  the  cars  run  at  frequent  intervals,  however,  such  cir- 
culating currents  will  not  have  to  flow  over  sufficiently  great  dis- 
tances in  the  tracks  to  cause  nearly  as  large  track  drops  as  would 
occur  with  the  same  loads  under  two-wire  operation.  The  result 
would  be  that  where  load  conditions  are  reasonably  favorable  for 
the  three- wire  system,  large  reductions  in  potential  drops  in  the 
negative  return  could  be  secured. 

While  almost  perfect  electrolysis  conditions  could  be  obtained 


58 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 


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DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  59 

with  the  parallel  three-wire  system,  the  difficulty  of  properly  in- 
sulating the  two  trolley  wires  from  each  other,  especially  at  cross- 
ings and  switches,  has  been  considered  so  great  that  the  sectional- 
ized  three-wire  system  is  considered  the  more  practicable  and  has 
therefore  been  employed  in  all  installations  which  have  come  to 
our  attention.  It  is  shown  diagrammatically  in  Fig.  15. 

In  this  form  the  feeding  district  is  divided  into  sections,  and 
alternate  sections  are  supplied  by  feeders  running  from  the  positive 
bus,  while  the  remaining  sections  are  supplied  by  feeders  from  the 
negative  bus,  the  difference  of  potential  between  the  two  buses 
being  approximately  1,200  volts.  In  this  way,  the  existence  on  the 
same  portion  of  the  street  of  two  trolleys  having  a  high  difference 
of  potential  between  them  is  avoided.  The  tracks,  as  before, 
serve  as  the  neutral  conductor  and  convey  the  current  from  the 
cars  in  one  section  to  those  in  the  adjoining  section  and  return  the 
unbalanced  current  to  the  powerhouse. 

(b)  Insulation  of  Trolley  Sections.     The  problem  of  insulating 
the  positive  and  negative  trolley  sections  from  each  other  is  one 
that  will  require  considerable  care.     At  points  of  simple    junc- 
ture this  has  been  accomplished  in  some  cities  by  the  use  of 
two  standard  600-volt  trolley  section  insulators  in  series,  with 
a  dead  section  of  trolley  wire  from  4  to  6  feet  in  length  between 
them.     In  other  cities  the  two  section  insulators  are  brought  to- 
gether, thereby  simplifying  the  overhead  construction.     It  is  also 
possible  to  use  a  single  1,200- volt  section  insulator  18  to  24  inches 
long.     Where  trolley  wires  of  opposite  polarity  cross,   it   will 
probably  be  found  better  to  make  the  entire  intersection  of  one 
polarity  rather  than  try  to  insulate  the  crossings.     At  the  inter- 
section of  two  double-track  lines  this  will  mean  the  installation 
of  four  double  section  insulators  as  just  described.     Where  such 
changes  are  made,  the  more  important  of  the  two  lines  should  be 
made  the  continuous  one  to  avoid  interruption  of  service  due  to 
failure  of  power  on  the  other  line.     Warning  signs  should  be  hung 
on  the  span  wire  at  all  section  insulators  and  motormen  should  be 
instructed  to  coast  across  these  points. 

(c)  Costs.     The  principal  economy  resulting  from  the  installa- 
tion of  the  three-wire  system,  is  the  saving  in  track  losses,  which 
are  greatly  reduced,  although  not  entirely  eliminated,  while  there 
usually  will  be  increased  station  losses  due  to  the  necessity  of 
always  operating  two  sets  of  generators  or  converters. 

In  systems  having  a  relatively  small  number  of  multiple  unit, 
power  supply  stations,  the  cost  of  converting  a  system  for  three- 


60  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

wire  operation  is  usually,  but  not  always,  smaller  than  the  first 
cost  of  insulated  negative  feeders,  or  any  other  measure  that  will 
give  the  same  degree  of  protection  from  electrolysis.  The  avail- 
able data  on  three-wire  systems,  both  as  to  costs  and  effects  of 
electrolysis  conditions  are  not  sufficient  to  warrant  the  laying 
down  of  general  rules  as  to  the  extent  of  its  application.  The 
local  factors  involved  in  each  case  are  often  peculiar  and  require 
special  consideration. 

In  cities  where  uninsulated  negative  copper  has  been  installed, 
it  may  be  reclaimed  after  conversion  to  three- wire  operation, 
unless  it  has  been  installed  under  pavement  or  embedded  in  con- 
crete, and  the  salvaged  copper  may  largely,  if  not  entirely,  cover 
the  cost  of  conversion. 

It  is  good  practice  to  provide  an  additional  bus  in  the  supply 
station  for  the  generators  and  feeders  operated  with  reverse 
polarity.  Double  throw  switches  are  also  installed  for  these 
feeders  and  generators. 

(d)  Difficulties  and  Limitations.  One  difficulty  which  some- 
times will  be  encountered  in  three-wire  operation  is  that  of  re- 
duced station  capacity,  as  two  or  more  machines  operating  in 
parallel  will  have  a  much  greater  capacity  at  times  of  excessive 
demand  than  when  divided  on  two  independent  circuits.  Heavy 
interurban  trains,  particularly  when  starting,  often  demand  the 
full  capacity  of  a  supply  station  and  the  same  condition  exists  at 
times  of  unusual  loads,  such  as  occur  after  a  tie-up  or  following  a 
ball  game  or  circus.  Where  the  generating  capacity  of  both  the 
positive  and  negative  sides  of  the  system  is  large  in  comparison  to 
the  maximum  demand  of  any  trolley  section,  this  objection  does 
does  not  exist,  but  where  only  a  single  small  machine  is  available 
for  one  side  of  the  load,  considerable  difficulty  may  be  encountered 
in  taking  care  of  the  peak  demands  under  extreme  conditions. 
Where  necessary  these  extreme  peak  demands  can  be  taken  care 
of  by  operating  all  of  the  machines  on  one  polarity  during  this 
period.  Double  throw  switches,  by  which  this  can  quickly  and 
conveniently  be  accomplished,  are  usually  provided  with  three- 
wire  operation. 

One  instance  of  an  overload  with  three-wire  operation  resulted 
in  the  too  frequent  blowing  of  the  circuit  breaker  on  the  negative 
generator.  This  was  eventually  overcome  by  installing  a  series 
resistance  which  is  automatically  cut  into  the  circuit  when  the 
current  reaches  a  predetermined  maximum  value,  thereby  limiting 
the  current  to  a  fixed  amount.  The  equipment  used  for  this  pur- 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  61 

pose  is  identical  with  that  employed  for.  automatic  railway  sub- 
station control. 

Not  only  are  unusual  loads  of  short  duration  difficult  to  take 
care  of  with  three- wire  operation,  but  where  the  entire  capacity  of 
a  station  with  all  machines  in  parallel  is  required  to  carry  the 
normal  peak-load,  it  may  be  impractical  to  convert  for  three- 
wire  operation.  In  general,  it  will,  of  course,  be  difficult  to 
divide  the  positive  and  negative  loads  in  the  same  ratio  as  the 
capacities  of  the  two  groups  of  generators  assigned  to  them. 
Moreover,  the  load  factor  of  the  whole  system  is  always  greater 
than  that  of  any  part,  and  the  generators  when  divided  into 
groups  will  therefore  be  operating  at  poorer  load  factors  and  con- 
sequently at  lower  efficiencies  than. when  in  parallel.  Therefore, 
where  no  excess  generator  capacity  exists,  it  may  sometimes  be 
necessary  to  install  an  additional  unit  in  converting  a  system  for 
three- wire  operation. 

Owing  to  the  continual  movement  of  cars  from  one  trolley 
section  to  another  of  opposite  polarity,  there  is  a  considerable 
variation  in  the  track  potential  at  any  point.  This  is  particularly 
true  on  lightly  loaded  lines  and  results  in  wide  fluctuations,  and 
even  reversals,  between  the  tracks  and  adjacent  underground 
structures.  While  the  algebraic  average  values  of  such  potential 
differences  may  be  greatly  reduced  by  the  adoption  of  a  three-wire 
system,  a  continuously  negative  condition  of  underground  struc- 
tures cannot  ordinarily  be  expected. 

Other  difficulties  of  less  importance  have  been  suggested:  (1) 
Some  equipment,  such  for  example  as  arc-headlights,  ampere- 
hour-meters  and  auxiliary  battery  control,  requires  a  single 
polarity  for  its  successful  operation.  Where  such  equipment  is 
used  it  will  be  necessary  to  provide  reversing  switches.  (2)  Two 
trolley  poles  in  parallel  cannot  be  employed  on  a  single  car  or  on 
trains  as  they  would  bridge  trolley  sections  of  opposite  polarity 
when  moving  across  section  breakers.  (3)  A  negative  trolley 
would  change  the  character  of  the  electric  arc  used  on  tracks  for 
arc- welding  and  building  up  joints  and  in  some  operations  might 
be  objectionable.  (4)  Commercial  customers  receiving  power 
from  trolley  feeders  may,  in  some  cases,  be  inconvenienced  by  a 
change  of  polarity. 

(e)  Practicability.  None  of  the  difficulties  here  cited  can  be 
considered  of  insurmountable  character,  and  like  many  other 
things,  the  system  can  be  made  to  work  satisfactorily  if  the  neces- 
sary attention  is  given  to  it.  Experience  has  fully  demonstrated 


62  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

that  it  will  greatly  improve  electrolysis  conditions  when  properly 
applied  and  also  give  better  operating  voltage  at  the  cars.  How- 
ever, to  secure  the  best  possible  results  with  this  system,  it  will 
often  be  necessary  to  change  feeder  copper  and  shift  section  in- 
sulators to  obtain  the  desired  sectionalization 

.  (f)  Extent  oj  Adoption,  Until  recent  years  the  three-wire 
system  has  not  been  employed  for  street  railway  work  in  this 
country,  although  it  has  been  in  use  in  Brisbane,  Australia,  and 
Nuremberg,  Germany,  for  a  number  of  years.  In  the  last  few 
years  it  has  received  some  attention  in  America  and  is  now  in 
operation  in  Omaha,  Wilmington,  Winnipeg,  Canada,  and  in  some 
portions  of  Los  Angeles  and  Milwaukee. 

The  Los  Angeles  installation  has  been  in  operation  since  1915 
and  more  recently  has  been  extended  to  include  several  additional 
station  districts.  In  Omaha  a  trial  installation  in  one  station 
district  was  made  early  in  1917.  After  several  months'  trial  with 
the  experimental  installation,  the  main  station  district  was  con- 
verted for  three-wire  operation  and  has  since  been  so  operated. 

Three-wire  operation  was  adopted  in  Winnipeg  as  a  means  of 
meeting  the  requirements  of  a  law  passed  by  the  Manitoba  Legis- 
lature, prescribing  certain  limitations  in  track  voltage  drops. 
Two  substation  districts  were  changed  over  in  1919,  and  since 
that  time  practically  the  entire  system  has  been  converted  to 
three-wire  operation. 

In  1920,  after  considerable  experimenting,  a  three-wire  system 
was  substantially  completed  in  Wilmington,  Delaware,  and  a 
complete  electrolysis  survey  made  under  both  two-wire  and  three- 
wire  operation.  With  the  latter,  a  considerable  improvement  in 
car  operation  due  to  higher  average  voltage  was  reported,  and 
also  better  electrolysis  conditions  on  water  and  gas  pipes.  Stray 
currents  and  overall  potentials  were  reduced  to  about  one-half 
their  values  with  two- wire  operation.  Reversing  potentials  were 
found  on  the  telephone  cables  in  some  areas  and  some  adjustment 
of  the  drainage  of  this  system  will  be  necessary  before  it  can  be 
said  to  be  entirely  satisfactory. 

3.  Reversed  Polarity  Trolley  System. 

This  method  of  railway  operation  involves  using  the  running 
tracks  as  the  positive  conductor  instead  of  the  trolley  wire. 
It  has  at  various  times  been  suggested  as  a  means  of  electrolysis 
mitigation,  and  in  at  least  one  case  it  has  received  an  extended 
trial..  Fundamentally,  however,  it  is  not  a  mitigation  method, 


DESIGN,  CONSTRUCTION,  OPERATION,  HTC.  63 

because  it  merely  reverses  the  direction  of  the  stray  current  and  in 
no  way  affects  the  magnitude  thereof.  With  reversed  polarity  the 
same  amount  of  corrosion  will  result  as  with  normal  operation  and 
the  only  difference  will  be  the  localities  in  which  the  damage  will 
occur.  Under  normal  operation  using  the  running  tracks  as  the 
negative  conductor,  the  electrolytic  damage  will  generally  be  con- 
fined to  the  area  immediately  surrounding  the  direct  current  power 
station  or  the  track  feeder  connection  points.  With  reversed  po- 
larity, the  electrolytic  corrosion  will  be  scattered  over  the  out- 
lying districts  which  with  normal  polarity  would  constitute  a 
negative  area.  If  the  trolley  system  is  operated  with  reversed 
polarity,  it  is  extremely  difficult  to  effectively  drain  the  lead 
sheaths  of  underground  cable  systems,  because  there  is  no  definite 
point  of  low  potential  to  which  to  drain. 

In  1912  the  polarity  of  the  electric  street  railway  system  in 
New  Haven,  Connecticut,  was  reversed  making  the  running  tracks 
the  positive  conductor.  This  method  of  operation  was  adopted 
by  the  railway  company  in  order  to  afford  immediate  relief  to  the 
gas  works,  and  to  the  water  and  gas  piping  systems  in  the  central 
part  of  New  Haven,  where  very  serious  damage  was  occurring. 
It  was  then  thought  that  in  the  outlying  sections  the  damage  would 
be  less  concentrated,  and  also  failures  would  be  less  serious  and 
more  easily  repaired,  than  in  the  central  business  district.  It  soon 
became  evident  that  it  was  practically  impossible  to  adequately 
drain  the  underground  telephone  cable  system,  and  that  even  with 
reversed  polarity  the  general  electrolysis  conditions  of  the  water 
and  gas  piping  systems  were  still  far  from  satisfactory,  and  after  a 
trial  of  eight  years,  this  method  of  operation  was  abandoned. 

The  New  Haven  experiment  therefore,  indicates  that  the 
reversal  of  railway  polarity  to  rails  positive  is  merely  a  means  of 
relieving  dangerous  electrolysis  conditions  in  the  vicinity  of  the 
power  station,  at  the  expense  of  the  cable  and  piping  systems  at 
some  distance  from  the  station.  When  no  underground  cable 
systotns  are  involved,  reversed  polarity  is  useful  as  a  temporary 
means  of  immediate  relief  to  an  endangered  piping  system  in 
the  interval  immediately  preceding  the  installation  of  effective 
electrolysis  mitigation. 

4.  Periodic  Reversal  of  Trolley  Polarity. 

If  the  polarity  of  the  trolley  is  reversed  daily,  at  a  time  when 
the  load  on  the  system  is  a  minimum,  few  operating  difficulties 
will  be  encountered  and  some  improvements  in  electrolysis  condi- 


64 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 


tions  will  result.  It  is  obvious  that  pipes  in  any  locality  will  be  in 
a  positive  condition  only  half  as  long  as  with  normal  operation, 
and  there  may  also  be  a  further  reduction  of  electrolysis  due  to 
redeposition  of  the  corroded  metal  during  the  period  when  the 


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Variation  of  Coefficient  of  Corrosion 
of  Iron   with  Frequency 

Fig.  16. 

pipes  are  negative.  Laboratory  experiments  made  by  the  Bureau 
of  Standards,  the  results  of  which  are  shown  in  Fig.  16,  indicate 
that  with  a  daily  reversal  of  polarity,  the  corrosion  of  iron  pipes 
at  any  point  will  be  about  twenty-five  per  cent  as  great  as  will 
result  without  such  reversals.  A  similar  relation,  though  not 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  65 

precisely  the  same  as  that  shown  in  Fig.  16  exists  with  respect  to 
lead  when  subjected  to  periodically  reversed  currents. 

This  method  of  operation  has  been  employed  by  the  Pacific 
Electric  Railroad  Company  of  Los  Angeles,  since  1918  in  Pomona, 
Redlands,  San  Bernardino,  Riverside,  and  Corona.  In  general  it 
is  not  applicable  to  cities  where  lead  cable  systems  are  installed 
underground,  as  it  would  greatly  complicate  and  sometimes 
render  impracticable  the  drainage  of  such  systems.  However, 
where  the  cable  system  is  small  and  confined  to  the  vicinity  of  the 
power  supply  station  it  may  be  drained  satisfactorily  through  an 
automatic  switch  which  permits  current  to  flow  from  the  cables, 
but  automatically  prevents  the  reversal  of  such  flow. 

Some  of  the  operating  difficulties  discussed  in  connection  with 
three-wire  systems  will  be  encountered  with  this  system.  The 
operating  difficulties  attending  a  more  frequent  reversal  of  the 
trolley  potential  would  be  considerably  greater,  and  no  attempt 
so  far  has  been  made  to  do  this. 

5.  Double  Contact  Conductor  Systems. 

The  double  overhead  trolley  system  of  electric  traction  as  at 
present  used  in  Cincinnati,  and  the  corresponding  underground 
conduit  systems  as  used  in  Washington  and  in  parts  of  New  York 
City,  if  properly  maintained,  eliminate  the  danger  of  electrolysis. 
This  system  has  in  past  years,  been  strongly  urged  by  some  pipe 
owning  companies  and  engineers  who  believed  it  to  be  the  only 
method  by  which  complete  immunity  from  electrolysis  could  be 
obtained.  It  is  now  generally  recognized,  however,  that  a  sub- 
stantial degree  of  protection  can  be  obtained  by  less  expensive 
and  objectionable  methods  and  the  demand  for  the  double  contact 
conductor  system  is,  therefore,  not  being  pressed  at  the  present 
time.  The  chief  objections  to  its  use  are  the  cost  of  installation 
and  the  increased  operating  difficulties  which  it  involves,  as  well 
as  an  unsightly  appearance  of  the  streets  in  the  case  of  the  double 
overhead  trolley.  The  double  contact  underground  system,  as 
used  in  New  York  and  Washington,  not  only  removes  the  source 
of  stray  current,  but  requires  no  overhead  wiring  or  poles  and  in 
rare  cases  may  be  justified  or  required  for  that  reason  alone. 
Merely  as  a  means  of  electrolysis  mitigation,  the  increased  cost 
of  the  double  contact  conductor  system  does  not  appear  to  be 
justified. 


66  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

II.  UNDERGROUND  STRUCTURES  SUBJECT  TO 
INJURY  BY  STRAY  CURRENTS 

A.    LOCATION  WITH  RESPECT  TO  TRACKS 

In  general,  the  problem  of  protection  from  stray  currents  has 
to  do  with  conditions  under  which  the  affected  structures  and  the 
tracks  are  already  in  place,  that  is,  where  their  respective  locations 
are  fixed.  In  the  great  majority  of  instances,  therefore,  a  dis- 
cussion of  the  most  favorable  relative  location  of  underground 
structures  and  rails  can  have  but  little  more  than  an  academic 
interest.  However,  in  laying  new  underground  structures  or 
replacing  old  ones,  it  is  in  the  interest  of  safety  to  locate  them  at 
as  great  a  distance  from  the  rails  as  possible.  Usually  condi- 
tions other  than  electrolysis  determine  the  location  of  mains, 
but  where  it  is  possible  to  locate  mains  on  both  sides  of  a  street 
having  car  tracks,  such  construction  prevents  the  crossing  of 
service  pipes  under  tracks  and  is  in  the  interest  of  good  electrolysis 
conditions.  Where  mains  or  services  must  cross  under  tracks 
there  is  a  considerable  advantage  in  having  them  as  deep .  as 
possible,  but  a  depth  of  more  than  4  or  5  feet  is  ordinarily  not 
justified. 

B.     CABLE  SYSTEMS 

1.  Avoidance  of  Accidental  Contacts  with  Other  Structures. 

From  an  electrolysis  standpoint,  it  is  usually  necessary  to  treat 
lead  sheath  cables  as  distinct  from  other  underground  structures 
due  to  the  fact  that  lead  is  appreciably  more  susceptible  to  corro- 
sion from  stray  current  than  iron,  and  also  because  different 
measures  are  usually  applied  to  the  protection  of  lead  sheath 
cables  than  to  other  underground  metallic  structures.  One  am- 
pere flowing  steadily  for  a  year  will  carry  into  solution  about  20 
pounds  of  iron  or  about  74  pounds  of  lead.  This  high  electro- 
chemical equivalent  of  lead  and  the  thin  walls  ordinarily  used  for 
cable  sheaths  require  that  unusual  care  be  exercised  in  their 
protection. 

In  the  Bell  Telephone  System  precautions  are  taken  to  avoid 
contact  between  its  lead  sheathed  cables  and  other  underground 
structures,  such  as  foreign  cables,  rails,  steel  bridges,  gas  or  water 
piping  system  and  the  metallic  structure  of  steel-frame  buildings. 
Where  it  is  necessary  that  cables  cross  a  bridge  structure,  this  is 
frequently  accomplished  in  creosoted  wood  duct.  Occasionally, 
however,  iron  pipes  are  used  to  conduct  cables  across  a  steel  bridge, 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  67 

but  where  this  is  done,  these  pipes  are  supported  so  that  they  are 
insulated  from  the  metal  work  of  the  bridge. 

2.  Conduit  Construction. 

Cable  sheaths  cannot  be  said  to  be  insulated  from  earth  even 
when  installed  in  non-conducting  duct  material,  but  as  compared 
with  pipes  which  are  laid  directly  in  the  earth,  their  resistance 
to  ground  is  generally  very  high.  Unless  surrounded  with  mud  or 
water,  cable  sheaths  usually  make  a  line  contact  with  the  duct 
walls,  whereas  pipes  make  a  surface  contact  of  much  greater  area. 

The  study  of  the  insulation  of  cable  sheaths  from  earth  there- 
fore resolves  itself  into  a  study  of  suitable  conduit  construction 
methods  since  experience  has  demonstrated  the  failure  of  any  sort 
of  wrappings,  dips,  or  coatings  to  afford  protection  of  any  value 
from  electrolysis.  Indeed,  wrappings,  dips,  and  coatings  have 
been  shown  to  be  distinctly  harmful  where  pipes  or  cables  are 
positive  to  the  earth  since  they  tend  to  localize  the  discharge  of 
current  and  thus  to  accelerate  failures. 

(a)  Signal  Cables.  The  experience  of  the  Bell  Telephone 
System  has  demonstrated  that  multiple  and  single  vitrified  clay 
duct  and  creosoted  wood  duct  are  all  equally  good  as  duct  material 
from  the  standpoint  of  electrolysis,  their  choice  in  specific  cases 
being  a  question  of  supply  and  cost.  Iron  pipe  is  occasionally 
used,  but,  due  to  its  cost,  only  when  necessary  in  avoiding 
obstructions. 

When  iron  pipe  is  used,  it  is  so  laid  that  there  will  be  no  contact 
between  it  and  the  trolley  rails,  steel  bridges,  water  pipes,  gas 
pipes  or  other  underground  structures  or  the  metal  work  of  build- 
ings. When  iron  pipes  must  be  laid  as  conduit  so  close  to  rails 
or  other  grounded  metallic  structures  that  a  separation  of  at 
least  one  foot  of  earth  cannot  be  obtained,  the  pipes  are  separated 
from  the  rails  or  other  grounded  metallic  structures  by  a  layer  of 
concrete  or  creosoted  plank  Three  inch,  vitrified  sewer  tile  with 
cement  joints  is  now  being  commonly  used  for  laterals  to  poles  or 
building  connections. 

In  good  conduit  construction  the  necessity  is  recognized  of 
rendering  the  joints  between  lengths  of  duct  material,  sufficiently 
tight  to  prevent  the  infiltration  of  dirt  and  silt  and  also  to  maintain 
a  sufficient  slope  to  the  conduit  to  insure  good  drainage  toward 
manholes,  the  manholes  in  turn  being  drained  by  sewer  connections 
or  to  sumps.  Particular  care  is  exercised  to  prevent  dips  or 
pockets  in  conduit  runs  where  moisture  might  collect.  It  is  the 


68  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

practice  to  rack  cables  in  manholes,  a  free  space  of  twelve  inches 
being  maintained  between  the  lowest  cable  and  the  manhole 
floor.  The  cables  are  in  metallic  contact  with  the  metal  hanger 
which,  in  turn,  may  be  in  contact  with  or  built  into  the  manhole 
wall,  experience  having  indicated  that  no  appreciable  increase  in 
cable  resistance  to  earth  is  obtained  by  insulating  the  cables  at 
these  points  with  porcelain  or  other  insulating  material. 

Where  lateral  cables  enter  buildings,  it  is  the  usual  practice 
in  the  Bell  System  to  avoid  all  contact  between  the  cable  and  the 
metal  structures  of  buildings,  and  wherever  this  is  impracticable, 
the  continuity  of  sheaths  on  the  entering  cables  is  broken  by  an 
insulating  joint. 

Occasionally  conduit  runs  must  be  built  through  swampy 
ground  or  along  sections  of  the  coast  where  the  conduit  is  per- 
manently below  sea  level.  Where  such  conditions  are  encountered, 
no  method  is  practically  possible  for  insulating  cable  sheaths  from 
earth  and  such  insulation  is  not  attempted.  Such  locations  are 
frequently  extremely  troublesome  from  the  electrolysis  standpoint, 
and  therefore  special  precautions  have  to  be  taken. 

(b)  Power  Cables.  The  practice  in  conduit  construction  for 
light  and  power  cables  is  somewhat  different  from  that  used  for 
signal  cables  because  the  former  are  characterized  by  necessity 
of  providing  for  troubles  originating  within  the  cables  and  for 
the  dissipation  of  the  heat  losses  of  the  cable.  The  most  common 
types  of  duct  material  used  are  single  duct  vitrified  tile,  multiple 
duct  vitrified  tile,  fibre  conduit  and  stone  conduit.  Iron  pipe  is 
frequently  used  for  short  laterals  to  buildings  and  for  cable  pole 
connections,  and  occasionally  where  on  account  of  lack  of  space 
other  types  cannot  be  installed.  It  is  a  common  practice  to  in- 
stall a  3-inch  concrete  envelope  entirely  surrounding  all  types  of 
power  conduits.  Multiple  conduit  made  up  of  single  duct  tile 
is  laid  with  staggered  joints  and  in  the  case  of  the  fibre  and  stone 
conduit,  the  ducts  are  separated  by  an  inch  or  more  of  concrete. 
Fibre  duct  is  generally  considered  as  a  mold  for  the  concrete  which 
latter  is  depended  upon  for  strength  and  for  the  separation  of  the 
cables  in  the  several  ducts. 

The  waterproofing  of  underground  conduits  for"  the  purpose  of 
excluding  moisture  and  improving  the  conditions  regarding  elec- 
trolysis was  tried  a  number  of  years  ago,  but  it  was  very  expensive 
and  found  to  be  quite  useless  unless  the  manholes  also  could 
be  waterproofed,  and  this  did  not  appear  to  be  practicable. 

The  report?  of  the  effect  of  the  different  types  of  duct  on  elec- 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  69 

trolysis  conditions  vary  considerably,  but  this  is  probably  due  to 
the  nature  of  the  soil  in  which  the  conduits  are  located,  the  amount 
of  moisture  in  the  soil  and  the  character  of  the  paving  under 
which  the  conduits  are  installed.  In  those  locations  where 
the  conduit  is  located  in  flat  country  with  poor  drainage  and  with 
the  natural  water  level  only  slightly  below  the  level  of  the  con- 
duits, the  effect  of  the  dirt  and  moisture  in  the  ducts  and  the 
dampness  in  the  surrounding  earth  is  to  lower  the  resistance  of 
the  cables  to  earth  so  that  this  value  is  not  materially  greater 
than  it  would  be  if  they  were  installed  directly  in  the  earth.  In 
other  locations  where  the  surface  of  the  ground  is  hilly  or  suffi- 
ciently undulating  to  afford  good  drainage  facilities,  the  cables 
installed  in  ducts  with  a  concrete  envelope  are  fairly  well  insulated 
from  the  earth. 

Although  iron  pipe  is  not  generally  used  in  line  conduits,  it  is 
frequently  necessary  to  employ  it  for  laterals  from  manholes  to 
poles  and  buildings,  in  order  to  avoid  obstructions  or  to  comply 
with  requirements.  If  used  as  conduits  for  drained  cable  sys- 
tems, iron  laterals  will  increase  the  danger  to  gas  and  water  ser- 
vice pipes  which  they  cross.  They  also  lower  the  resistance  be- 
tween the  earth  and  cable  sheaths  which  they  contain  and  there- 
by enable  the  cables  to  pick  up  larger  amounts  of  stray  current 
than  they  otherwise  would. 

In  order  to  afford  the  return  current  a  metallic  path  to  the 
station  in  case  of  the  failure  of  the  cable,  it  is  the  standard  practice 
with  many  companies  to  connect  the  lead  sheaths  of  all  of  their 
cables  in  every  manhole.  This  serves  also  to  prevent  serious 
differences  in  potential  between  the  lead  sheaths  of  cables  in  the 
same  conduit  at  the  time  of  a  burnout  and  the  resulting  damage 
to  lead  sheaths  in  adjacent  ducts  which  would  otherwise  occur. 

Where  metal  cable  racks  are  used  in  manholes  it  is  a  frequent 
practice  to  insulate  the  cables  from  such  racks,  this  being  done 
to  prevent  damage  from  electrolysis  as  well  as  to  prevent  damage 
in  case  of  a  burnout  of  one  of  the  adjacent  cables. 

Unless  necessary  as  a  protective  measure  for  isolated  sections, 
cable  sheaths  should  not  be  artificially  grounded.     Grounds  in 
negative  areas  through  which  stray  current  might  be  picked  up 
should  be  avoided  wherever  practicable. 
3.  Surface  Insulation. 

In  the  early  days  of  the  use  of  lead  covered  cables  for  light 
and  power  in  this  country,  it  was  customary  to  have  the  lead 
covered  cables  incased  in  a  wrapping  of  jute  saturated  with  a  pre- 


70  DESIGN,  CONSTRUCTION,  OPERATION,  ETC, 

servative  compound  with  the  idea  of  preventing  damage  to  the 
cables  by  electrolysis.  While  this  may  have  been  fairly  satis- 
factory as  a  temporary  expedient,  the  preservative  compound  in 
the  course  of  time  would  gradually  disappear  and  the  rotting  of 
the  jute  would  follow.  In  pulling  such  cables  out  of  the  ducts,  it 
was  found  in  some  cases  that  the  jute  was  so  badly  rotted  that 
it  could  not  be  left  on  the  cables  when  they  were  reinstalled  in 
another  location,  and  in  other  cases,  the  jute  would  adhere  to 
the  ducts  or  become  caught  on  the  edges  of  the  ducts  and  form  a 
very  serious  obstacle  to  the  removal  of  the  cable.  Moreover, 
coatings  of  this  character  are  not  always  a  protection  against 
electrolysis  and  may  even  accelerate  it  by  localizing  the  corrosion, 
as  explained  in  the  discussion  of  surface-  insulation  for  pipes.  On 
account  of  these  difficulties,  the  use  of  the  jute  covering  on  the 
lead  covered  underground  cables  was  generally  abandoned  some 
years  ago. 

4.  Insulating  Joints. 

Some  light  and  power  companies  have  used  insulating  joints 
for  protecting  their  cables  from  electrolysis.  In  some  cases  each 
section  was  connected  to  a  ground  pipe  or  plate  under  the  floor 
of  the  manhole.  If  the  conditions  were  favorable  for  electrolytic 
action,  these  ground  plates  or  pipes  served  merely  as  auxiliary 
anodes  and  would  be  destroyed  by  electrolytic  action  in  the  course 
of  a  few  years,  thus  rendering  them  ineffective  except  at  a  con- 
siderable annual  expense  for  maintenance.  Partly  for  this  reason, 
but  more  because  of  the  general  adoption  of  cable  drainage  as  a 
method  of  electrolysis  mitigation,  the  use  of  insulating  joints 
for  protecting  lead  covered  cables  for  light  and  power  purposes 
has  been  practically  abandoned  in  this  country. 

As  the  drainage  of  cables  requires  continuous  lead  sheaths, 
insulating  joints  are  not  now  ordinarily  used  in  cable  systems. 
With  drainage  it  is  also  desirable  that  the  several  cables  in  any 
duct  system  be  bonded  together  in  the  manholes  so  that  all  cables 
may  be  equally  drained  and  also  that  in  case  of  a  failure  of  one 
cable  the  current  through  the  fault  to  the  sheath  can  find  a  con- 
tinuous metallic  return  path  to  the  station.  If  the  insulation 
fails  on  a  cable  with  an  isolated  lead  sheath,  the  potential  of  the 
sheath  will  become  approximately  that  of  the  conductor  and 
destructive  arcing  may  occur  at  the  insulating  joints,  and  in  addi- 
tion, holes  will  be  burned  in  the  lead  sheaths  of  the  cable  where 
it  is  in  accidental  contact  with  other  cables  or  where  it  rests  on 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  71 

metal  cable  racks  or  supports  in  manholes.  Where  insulating 
joints  are  used,  it  is  therefore  quite  necessary  to  ground  each  section 
of  the  sheath. 

Under  special  conditions  insulating  joints  can  sometimes  be 
used  to  advantage  in  protecting  cables  from  electrolysis,  as  for 
example,  when  the  cables  are  remote  from  any  railway  tracks  or 
negative  return  circuit  to  which  they  can  be  drained,  or  where  a 
cable  system  which  is  not  drained  can  be  prevented  from  collecting 
stray  current  at  points  of  intersection  with  railway  tracks  by 
their  use.  Fig.  17  shows  the  type  of  insulating  joint  used  by 
several  large  electric  power  companies  in  the  sheaths  of  trans- 
mission cables  which  are  not  protected  by  drainage. 

Another  situation  sometimes  requiring  insulating  joints  in 
order  to  prevent  cables  from  picking  up  excessive  current,  or  to 
prevent  arcing,  is  to  be  found  where  they  make  contact  with  a 
steel  bridge  or  are  otherwise  brought  into  intimate  contact  with 
the  earth.  Under  such  conditions  the  section  making  contact  can 
be  isolated  by  the  use  of  insulating  joints  and  continuity  of  the 
system  maintained  by  bonding  around  the  section  so  isolated. 
Such  conditions  as  these,  however,  are  comparatively  rare. 

Insulating  joints  in  lead  sheaths  are  not  only  expensive  but 
represent  points  of  discontinuity  which  may  give  rise  to  various 
troubles  and  are  usually  avoided  in  practice  except  under  such 
unusual  conditions  as  are  here  mentioned. 

C.  PIPE  SYSTEMS 

1.  Surface  Insulation. 

In  the  cities  where  there  is  trouble  from  electrolysis,  the  service 
pipes  of  the  gas  and  water  companies  are  more  subject  to  failure 
than  the  cast  iron  mains  as  the  walls  of  the  wrought  iron  pipes 
are  much  thinner.  Also,  in  the  electrolytic  corrosion  of  cast 
iron  pipe  a  graphitic  residue  remains  intact  and  has  a  strength 
sufficient  to  withstand  gas  pressure  and  in  some  cases  even  low 
water  pressure,  while  with  wrought  iron  or  steel  the  metal  is 
corroded  away  without  leaving  such  a  residue.  For  these  reasons 
some  gas  companies  have  made  it  a  practice  to  apply  a  surface 
covering  to  their  service  pipes.  This  covering  is  generally  similar 
to  that  described  above  for  lead  covered  cables,  but  it  sometimes 
consists  of  several  layers  of  jute,  burlap,  cheese  cloth,  or  paper,  each 
of  which  has  an  application  of  insulating  preservative  compound 
before  applying  the  next  layer.  Such  insulating  coverings  have 
been  more  successfully  applied  to  services  than  to  lead  covered 


72 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 


"5-8 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  73 

cables.  The  expense  of  this  covering  usually  precludes  its  use  for 
cast  iron  mains,  although  it  is  sometimes  applied  to  wrought  iron 
or  steel  gas  mains. 

The  principal  difficulty  in  coatings  applied  to  pipes  or  lead 
cable  sheaths  is  that  the  coatings  are  not  continuous  and  that  in 
spite  of  all  efforts  for  their  prevention  minute  holes  or  pores  will 
exist  in  such  coatings.  Through  these  minute  pores  the  electrolyte 
will  ultimately  penetrate  and  electrolytic  action  will  result.  As 
the  amount  of  pipe  or  cable  surface  exposed  through  these  pores 
is  small,  the  action  will  be  very  slow  at  the  start  and  it  may  be  quite 
imperceptible  for  a  number  of  months.  In  the  course  of  time, 
however,  if  the  conditions  are  favorable  for  electrolysis,  an  oxide 
of  the  metal  will  be  formed  opposite  the  pores  and  as  the  oxide 
occupies  more  space  than  the  metal,  the  coating  will  be  lifted  from 
the  metal,  thus  rapidly  increasing  the  area  of  metal  exposed  to 
the  electrolytic  action.  As  this  action  is  concentrated  at  a  com- 
paratively few  points  by  the  coating,  the  result  is  that  the  destruc- 
tion of  the  pipe  or  cable  may  occur  more  rapidly,  due  to  this 
intensified  local  action,  than  would  occur  if  the  pipe  or  cable  was 
without  such  coatings  so  that  the  action  would  be  distributed 
over  the  entire  area  of  pipe  or  cable. 

Surface  insulation  for  the  protection  of  pipes  and  cables  against 
soil  or  salt  water  corrosion  is  often  effective,  but  as  described 
above,  these  coatings  gradually  deteriorate  when  subjected  to 
any  appreciable  potential  difference. 

Thick  coatings  in  the  form  of  pitch  or  parolite  poured  into  a 
containing  box  built  around  the  pipe,  have  been  used  successfully 
in  special  cases.  The  box  should  be  quite  strong  so  as  not  to  sag 
beneath  the  weight  of  the  insulating  material  while  pouring  or 
after  back-filling.  The  pipe  should  be  supported  in  this  box  by 
means  of  blocks  of  glass  or  of  pitch  impregnated  wood,  so  as  to 
prevent  its  exposure  in  the  event  of  the  cold-flow  of  the  insulating 
material.  In  pouring,  extreme  care  must  be  exercised  to  prevent 
particles  of  earth  or  stone  from  getting  into  the  box,  and  the 
insulating  material  should  be  hot  enough  to  flow  freely  without 
boiling  or  bubbling.  If  it  is  too  hot,  the  boiling  or  bubbling  will 
result  in  air  holes  when  the  material  solidifies,  and  these  air  holes 
may  admit  moisture  to  the  pipe.  If  the  pipe  to  be  covered  is 
laid  on  a  grade,  or  if  it  is  more  than  25  feet  long,  it  will  be  neces- 
sary to  pour  the  material  in  sections,  using  dams  made  of  pitch 
impregnated  wood  to  retain  the  molten  material.  The  material 
should  cover  the  pipe  to  a  depth  of  about  two  inches  and  a  rigid 


74  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

cover  should  be  placed  on  top  of  the  box  or  trough  to  prevent 
stones  or  earth  from  working  their  way  through  the  insulating 
material.  This  boxing  method  is  also  applicable  to  service  or 
other  small  pipes,  and  while  somewhat  more  expensive,  it  is  pre- 
ferable to  the  wrapping  method  because  in  its  application  there 
are  fewer  chances  of  imperfections  escaping  detection. 

Too  much  care  cannot  be  exercised  in  applying  insulating  cover- 
ings in  regions  where  there  is  a  strong  tendency  for  current  to 
leave  the  pipe.  A  single  imperfection  through  which  moisture 
can  reach  the  pipe  will  cause  it  to  be  destroyed  more  rapidly  with 
the  covering  than  without  it.  As  an  additional  precaution  where 
insulating  covering  is  applied  in  a  positive  area,  insulating  joints 
are  often  installed  in  the  pipe  at  each  end  of  the  covering.  If 
the  covered  section  is  more  than  2,000  feet  long,  additional  in- 
sulating joints  should  be  installed  at  intermediate  points. 

The  application  of  insulating  covering  is  not  always  limited 
to  the  positive  areas  in  which  current  tends  to  leave  the  pipe. 
They  are  quite  often  used  to  prevent  current  reaching  the  pipe, 
in  negative  areas,  where  a  pipe  crosses  or  comes  near  to  a 
trolley  line  or  other  underground  metallic  structures  to  which  it  is 
highly  negative. 

The  costs  of  installing  insulating  coverings  of  the  character 
referred  to  will  vary  over  fairly  wide  limits,  depending  upon 
the  size  of  the  pipe,  the  length  to  be  covered,  the  character  of 
the  soil,  and  the  depth  of  the  pipe,  etc.  In  1915  the  cost  of 
boxing  and  covering  500  feet  or  more  of  8-inch  line  laid  at  a 
depth  of  about  30  inches  in  ordinary  soil  averaged  about  one 
dollar  per  foot.  In  1919  this  figure  had  increased  to  about  three 
dollars  per  foot. 

2.  Insulating  Joints. 

(a)  New  Work.  The  value  of  insulating  joints  in  pipes  as  a 
means  of  preventing  or  reducing  electrolysis  has  long  been  recog- 
nized, but  the  manner  of  employing  them  has  not  always  been 
such  as  to  accomplish  the  desired  end.  Their  effectiveness  will 
depend  very  largely  upon  the  frequency  with  which  they  are 
installed  in  any  pipe  line  and  somewhat  upon  other  factors,  such  as 
the  resistivity  of  the  soil,  the  magnitude  of  the  potential  gradient 
in  the  earth  and  the  degree  of  isolation  maintained  with  respect 
to  other  underground  structures. 

Current  flow  on  metallic  pipe  lines  can  be  practically  prevented 
by  using  a  sufficient  number  of  insulating  joints.  A  pipe  line 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 


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76  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

laid  with  every  joint  an  insulating  joint  has  a  comparatively 
high  resistance,  and  no  substantial  current  can  flow  on  such  a 
line. 

It  is  sometimes  possible  to  break  up  the  electrical  continuity 
of  the  line  and  substantially  protect  it  from  electrolysis  by  the 
use  of  a  comparatively  few  insulating  joints,  but  in  these  cases 
tests  should  be  made  to  see  that  the  longitudinal  flow  of  current 
along  the  pipe  has  been  practically  eliminated. 

The  services  can  be  prevented  from  making  electrical  contact 
with  other  systems  by  the  use  of  insulating  joints  within  the 
premises  served,  as  shown  in  Fig.  18.  Without  the  insulating 
joint  in  the  service  pipe,  stray  current  could  enter  from  the  other 
piping  system  and  injure  both  the  service  and  the  section  of  main 
to  which  it  connects. 

Some  gas  companies,  principally  natural  gas  companies,  have 
established  the  practice  in  all  new  work  of  insulating  services  at 
the  meter  connections  within  the  premises,  thus  preventing  the 
flow  of  current  between  gas  and  water  services.  If  this  is  generally 
applied  on  new  mains  of  considerable  length,  it  is  also  advisable 
to  install  insulating  joints  at  selected  locations  on  the  main. 

(b)  Cement  Joints.     Cement  joints  have  long  been  used  on 
gas  mains  and  have  been  found  to  preserve  a  high  resistance  over 
a  long  period  of  time,  and  if  used  in  sufficient  numbers  they  are 
effective  in  preventing  the  flow  of  stray  current  on  pipe  lines. 
The  standard  cast  iron   bell  has   been  used  successfully  with 
cement  joints  on  small  mains  but  some  gas  companies  have  had 
difficulty  in  using  cement  on  mains  12  inches  in  diameter  or  larger. 
Cast  iron  pipe  is  now  being  manufactured  with  the  bells  especially 
designed  for  cement  joints  so  that  they  can  be  used  on  large  size 
mains.     This  joint,  illustrated  in  Fig.  19,  is  known  as  the  type  B 
joint,  as  covered  by  the  specifications  of  the  Committee  on  Cast 
Iron  Pipe  Joints  of  the  American  Gas  Association.     The  calking 
recess  is  unusually  long  and  has  a  slight  taper  whereby  the  joints 
are  tightened  when  the  pipe  line  contracts.     When  properly  made, 
these  joints  have  a  mechanical  strength  considerably  in  excess  of 
the  pipe  itself. 

(c)  Leadite  and  Metallium.     Other  substitutes  for  lead,  such  as 
"Leadite"   and   "Metallium"   are  being  used  on  water  mains. 
Some  years  ago  the  Bureau  of  Standards  made  tests  on  "Leadite" 
joints  and  found  this  material  when  new  to  have  a  very  high 
electrical  resistance,  comparable  with  that  of  cement,  but  after 
several  years  in  service  to  decrease  in  resistance  to  only  a  very 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 


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78  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

mall  fraction  of  the  original  value.  The  change  was  attributed 
to  the  slow  oxidation  of  the  sulphur  contained  in  the  compound, 
resulting  in  the  production  of  sulphuric  acid.  No  corresponding 
data  are  yet  available  on  "Metallium." 

(d)  Dresser  Couplings  of  the  ordinary  type  which  have  been 
extensively  used  on  wrought  iron  and  steel  gas  mains  are  uncertain 
and  variable  in  their  resistance,  depending  upon  the  manner  in 
which  they  are  installed.     However,  if  used  throughout  any  pipe 
line  their  average  resistance  is  so  high  as  to  practically  eliminate 
the  flow  of  stray  current. 

(e)  Special  Insulating  Joints.     A  special  high  resistance  joint 
is  made,  known  as  the  "Dresser  Insulating  Coupling,"  and  is 
used  to  prevent  the  flow  of  stray  current  on  pipes.     Insulating 
joints,  such  as  wood  stave  joints,  and  flange  joints  with  insulated 
bolts  and  gaskets  of  insulating  material  are  sometimes  used  on 
large  mains  at  river  crossings  or  at  points  of  intersection  with 
street  railways  and  at  other  special  locations.     The  effective  length 
of  such  joints  can  be  increased  by  thoroughly  insulating  the  pipe 
with  wrappings  or  covering  for  some  distance  on  either  side  of  the 
joint.     This  treatment  is  often  applied  to  important  oil  and  high 
pressure  gas  pipe  lines. 

(f)  Insulating  Joints   Applied  to   Kxisting  Pipe   Lines.     Pipe 
lines  acting  as  ties  between  two  extensive  systems  or  networks 
sometimes  carry  considerable  current  from  one  system  to  the  other 
and  this  can  be  reduced  or  practically  eliminated  by  the  use  of 
comparatively  few  insulating  joints  installed  in  the  main  con- 
necting the  two  systems.     To  distribute  the  stray  current  around 
insulating  joints  so  installed,  the  joint  can  either  be  made  long  or 
the  pipe  insulated  for  some  distance  on  either  side. 

A  large  industrial  plant  or  a  small  community  may  be  supplied 
with  gas  or  water  through  a  single  pipe  over  which  stray  current 
may  flow  and  cause  damage  at  some  point  which  would  otherwise 
not  be  in  danger.  The  use  of  one  or  more  insulating  joints  will 
often  correct  such  a  condition  at  little  expense. 

A  pipe  line  crossing  under  an  electric  railway  track  or  through 
a  river  or  wet  ground  can  be  prevented  from  discharging  or 
collecting  current  at  such  points  by  the  use  of  insulating  joints 
on  both  sides  of  the  exposure. 

Service  pipes  which  are  subject  to  corrosion  at  points  where 
they  cross  under  railway  tracks  are  often  insulated  from  the  mains 
by  the  use  of  insulating  joints  at  times  of  replacements  thus  pre- 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  79 

venting  the  further  passage  of  current  from  the  main  to  the 
service. 

Insulating  joints  are  also  frequently  used  to  prevent  the  inter- 
change of  current  between  two  piping  systems,  as  shown  in  Fig. 
18,  or  between  a  piping  system  and  a  cable  system  or  other  under- 
ground structures.  In  order  to  protect  gas  services  or  water 
services  where  they  cross  under  tracks,  it  is  often  necessary  to 
install  insulating  joints  both  at  the  main  and  within  the  premises 
to  prevent  the  flow  of  current  from  services  of  another  system  to 
which  they  may  connect.  This  condition  exists  where  gas  water 
heaters  are  in  use  as  these  appliances  usually  make  a  firm  metallic 
contact  between  the  gas  and  water  services.  In  Fig.  20,  if  the 
gas  and  water  mains  are  both  positive  to  the  track,  accelerated 
corrosion  will  take  place  on  the  services  where  they  cross  under 
the  track.  To  protect  one  service  without  regard  to  the  other,  it 
is  obviously  necessary  to  install  insulating  joints  at  A  and  B,  or 
C  and  D. 

Insulating  joints  have  been  installed  at  selected  locations  by 
some  gas  and  water  companies  as  an  auxiliary  to  a  negative  feeder 
system.  For  example  in  Providence,  Rhode  Island,  after  an 
insulated  negative  feeder  system  was  put  in  operation  insulating 
joints  were  installed  on  gas  and  water  mains  to  still  further  reduce 
the  stray  current  on  the  pipes. 

The  cost  of  installing  insulating  joints  when  pipes  are  uncovered 
for  repair  or  replacement  is  comparatively  a  small  item,  and  often 
affords  a  satisfactory  means  of  preventing  further  damage  to 
them. 

3.  Shielding. 

In  special  cases  underground  structures  have  been  protected 
from  electrolysis  by  connecting  to  the  structure  an  auxiliary 
metallic  conductor  located  so  as  to  cause  the  current  to  flow  to 
earth  from  the  auxiliary  conductor.  This  mode  of  protection  is 
known  as  shielding.  The  method  has  in  some  cases  been  applied 
to  the  dead  end  of  an  underground  metallic  structure  which  is 
highly  positive  to  earth.  In  such  cases  an  auxiliary  shielding 
plate  or  pipe  of  adequate  ground  contact  surface  extending  beyond 
the  dead  end  and  electrically  connected  to  the  structure  to  be 
protected  has  been  installed  in  such  a  manner  that  the  bulk  of  the 
current  was  caused  to  leave  the  auxiliary  shielding  conductor,  thus 
affording  a  certain  degree  of  protection  to  the  dead  end  of  the 
structure.  One  application  of  this  method,  which  is  in  use,  is 


80 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 


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DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  81 

that  of  a  service  pipe  crossing  under  tracks  or  crossing  other 
structures  to  which  it  is  positive  and  where  the  pipe  comes  rela- 
tively close  to  the  rails  or  other  structures  at  the  point  of  crossing. 
In  these  cases  a  larger  shielding  pipe,  usually  of  heavy  cast  iron, 
has  been  placed  around  the  service  pipe  and  electrically  connected 
to  the  service  pipe  and  extended  sufficiently  on  each  side  of  the 
crossing  so  that  the  major  part  of  the  current  was  caused  to  leave 
the  shielding  pipe,  thereby  corroding  the  latter  while  protecting 
the  service  pipe. 

It  is  very  important  that  a  thorough  metallic  connection  be 
made  between  the  pipe  to  be  protected  and  the  shielding  pipe. 
Otherwise,  the  service  pipe  is  likely  to  corrode  where  current 
leaves  it  to  flow  through  earth  to  the  shielding  pipe.  Unless  the 
shield  is  in  the  form  of  a  pipe  completely  surrounding  the  structure 
to  be  protected,  this  method  of  protection  is  uncertain  and  should 
be  used  only  in  very  special  cases.  When  applying  this  method  it 
has  been  found  necessary  to  take  care  that  the  auxiliary  shielding 
conductor  does  not  merely  increase  the  electrode  area  from  which 
the  current  leaves,  because  in  this  case  the  current  will  continue 
to  leave  from  the  structure  which  is  to  be  protected  unless  an 
insulating  covering  is  applied  to  the  pipe  beyond  the  protecting 
shield.  This  has  been  found  to  be  the  practical  result  where  a 
shielding  conductor  of  the  same  or  less  contact  area  was  placed 
in  the  earth  near  the  structure  to  be  protected  and  where  the  stray 
current  has  left  both  structures. 

III.     MEASURES    INVOLVING    INTER-CONNEC- 
TION OF  AFFECTED  STRUCTURES  AND 
RAILWAY  RETURN  CIRCUIT 

A.  ELECTRICAL  DRAINAGE  OF  CABLE  AND  PIPE  SYSTEMS 

Electrical  drainage  consists  in  connecting  the  affected  structure 
to  the  railway  return  circuit  by  insulated  conductors  in  such  a 
manner  that  the  current  leaves  the  structure  through  these 
connections  instead  of  flowing  to  earth.  This  prevents  corrosion 
in  the  neighborhood  of  the  drainage  connections,  but  increases 
the  current  flowing  on  the  structure  and  the  voltage  drop  along  it, 
which  latter  results  are  generally  undesirable  for  reasons  discussed 
in  detail  in  subsequent  paragraphs. 

Drainage  connections  are  usually  made  by  running  copper 
cables  either  to  the  busbar  of  the  railway  supply  station  or  to 
negative  return  feeders.  Connections  to  tracks  should  be  avoided 


82  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

because  the  failure  of  rail  bonds  might  cause  dangerous  currents 
to  flow  over  the  drainage  connection  and  also  because  of  the  pos- 
sibility of  getting  a  current  reversal,  particularly  when  the  adjacent 
substation  shuts  down  during  the  light  load  period.  However, 
when  insulated  negative  feeders  are  used,  the  drainage  connections 
may  be  made  to  the  rail  terminals  of  the  feeders.  Connections 
to  rails  are  sometimes  installed  where  a  conduit  line  or  a  pipe 
crosses  a  railway  track  at  a  considerable  distance  from  the  power 
supply  station  and  other  means  of  draining  would  be  awkward 
and  expensive,  but  they  should  be  made  with  considerable  dis- 
cretion and  should  be  carefully  recorded  and  regularly  inspected. 

Where  used,  drainage  should  be  reduced  to  a  minimum  con- 
sistent with  the  protection  of  the  drained  structure  in  order  to 
reduce  the  hazard  to  other  adjacent  underground  systems. 

The  drainage  of  one  system  tends  to  establish  differences  of 
potential  between  the  various  underground  systems,  resulting  in 
interchange  of  current  with  consequent  injury  to  the  system  at 
the  higher  potential.  In  order  to  avoid  this  condition,  it  is  de- 
sirable to  interconnect  the  various  systems  and  drain  them  over 
common  conductors.  As  structures  owned  by  different  interests 
cannot  be  bonded  together  except  by  an  agreement  between  the 
owners  this  has  frequently  of  itself  made  it  impossible  to  apply  a 
comprehensive  drainage  system  to  all  structures  because  of  the 
impossibility  of  obtaining  an  agreement  of  all  owners  to  allow 
connections  to  their  structures,  except  on  condition  that  other 
interests  assume  liability  for  any  injury  which  may  result  from 
such  interconnections. 

If,  however,  the  foregoing  method  of  unified  drainage  is  carried 
out  so  that  the  drained  structures  are  at  all  times  negative  to 
earth,  no  electrolytic  corrosion  of  such  structures  will  result. 
Just  how  difficult  it  may  be  to  maintain  pipes  negative  to  earth 
at  all  points  and  at  all  times  by  means  of  drainage  is  a  question 
which  cannot  be  answered  until  investigations  have  been  carried 
further. 

The  objections  to  electrical  drainage  apply  most  forcibly  to 
pipe  networks,  particularly  to  gas  and  oil  pipes  on  account  of  the 
inflammable  substances  carried.  Drainage  should  be  considered 
only  as  a  supplementary  measure  to  the  improvement  of  the  rail- 
way return  circuit  or  as  a  temporary  measure  in  cases  where  acute 
electrolytic  corrosion  has  resulted.  It  can  never  take  the  place 
of  an  adequate  railway  return  circuit. 

Notwithstanding  its  numerous  disadvantages  and  limitations, 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  83 

there  are  engineers  who  believe  that  pipe  drainage  has  a  definite 
field  of  usefulness.  The  Committee,  through  its  Research  Sub- 
Committee,  is  still  actively  engaged  in  investigating  the  magni- 
tude and  importance  of  the  technical  factors  involved  and  until 
further  information  shall  have  been  acquired,  the  Committee  will 
not  be  in  a  position  to  reach  a  conclusion  on  this  subject. 
1.  Drainage  of  Cable  Sheaths. 

(a)  Method  of  Draining  Cable  Sheaths.  In  order  to  afford  com- 
plete protection  to  cable  systems,  it  has  been  found  that  they 
should  be  interconnected  and  have  drainage  conductors  of  sufficient 
conductivity  located  so  that  the  lead  sheath  of  the  cable  network 
is  everywhere  lower  in  potential  than  the  adjacent  earth.  Cable 
systems  are  usually  installed  in  vitrified  clay,  creosoted  wood, 
or  fibre  ducts,  and  if  kept  free  from  water,  the  tendency  to  collect 
current  is  much  less  than  if  they  were  in  direct  contact  with  the 
earth.  Owing  to  the  higher  resistance  thus  introduced  between 
cables  and  earth  and  the  continuous  character  of  the  cable  sheaths, 
it  is  usually  possible  to  lower  the  potential  of  the  system  below 
that  of  the  adjacent  earth  in  all  localities  by  draining  relatively 
small  currents  at  one  or  more  points. 

In  order  to  prevent  the  interchange  of  current  through  earth 
between  the  several  cable  sheaths  in  any  conduit  system,  it  is 
necessary  to  bond  the  sheaths  together  at  frequent  intervals. 
Some  companies  make  a  practice  of  bonding  at  every  manhole 
and  good  practice  requires  such  bonding  at  intervals  not  to  exceed 
five  hundred  feet.  Bonding  is  usually  accomplished  by  sweating 
a  flat  copper  strip  or  a  copper  cable  to  all  cables  within  any  system 
which  may  properly  be  bonded  together.  Foreign  cables  which 
enter  any  duct  system  are  also  bonded  to  the  system  they  parallel. 
It  is  often  necessary  to  interconnect  signal  cables  with  lighting  and 
power  cables  so  as  to  avoid  differences  of  potential  which  might 
otherwise  occur,  but  where  this  is  done,  a  fuse  should  be  installed 
in  the  bond  connection  to  the  signal  cable  so  as  to  eliminate  the 
possibility  of  high  voltage  current  getting  on  the  signal  cable 
sheaths. 

It  is  desirable  to  provide  means  for  measuring  all  drainage 
currents  and  where  the  drainage  feeder  is  extended  to  the  supply 
station,  an  ammeter  or  shunt  is  usually  installed  for  that  purpose 
within  the  station.  Where  the  drainage  cable  does  not  enter  the 
supply  station,  measurement  can  be  made  within  a  manhole  or  on 
a  pole,  or  wherever  the  drainage  cable  is  accessible. 

Where  a  cable  system  tends  to  become  positive  in  regions  remote 


84  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

from  the  railway  supply  station,  it  is  necessary  either  to  use  a 
long  copper  cable  for  drainage  at  a  considerable  expense  or  to 
resort  to  some  other  method  of  protection.  Aerial  telephone 
cables  are  sometimes  used  for  this  purpose,  but  are  not  employed 
except  when  other  conductors  are  not  available  or  would  be  unduly 
expensive. 

Cables  are  sometimes  found  to  be  positive  only  during  certain 
periods  of  the  day  or  their  potential  may  reverse  from  time  to 
time  due  to  fluctuations  in  the  railway  load.  Where  this  condition 
is  considered  dangerous  from  the  electrolysis  standpoint  an 
automatic  switch  is  sometimes  installed  which  is  closed  during  the 
period  the  cable  is  positive  and  automatically  opens  when  the 
cable  becomes  negative,  the  object  being  to  prevent  the  cable 
from  taking  on  current  while  in  a  negative  condition.  The  cost 
of  automatic  switches  and  the  fact  that  they  add  an  objectionable 
complication  to  the  plant  are  reasons  why  their  use  should  be 
restricted  as  much  as  possible. 

Automatic  or  manually  operated  switches  should  be  provided 
in  all  drainage  cables  terminating  in  railway  supply  stations  in 
order  that  they  may  be  opened  during  the  period  when  the  station 
is  not  in  operation.  Automatic  substations  which  start  and  stop 
without  attendants  should  be  provided  with  facilities  for  accom- 
plishing this  result. 

(b)  Heating  Effect  of  Stray  Current  on  Cable  Sheaths.  Stray 
current  on  the  sheaths  of  lead  covered  cables  causes  a  heating 
effect  which  impairs  the  carrying  capacity  of  power  cables.  In 
some  cases  this  effect  may  be  objectionable. 

The  following  formulae  have  been  developed  for  single  conduc- 
tor and  three  conductor  cables  to  give  their  current  carrying 
capacity  when  sheath  currents  flow.  The  values  obtained  give 
the  conductor  the  same  temperature  rise  above  surrounding 
structures  as  produced  by  their  normal  current  when  no  sheath 
currents  are  present. 

The  formulae  have  been  developed  on  the  following  basis: 

1.  That  the  watts  dissipated  in  the  sheath   are   effective  in 
raising  the  sheath  temperature  but  that  they  do  not  affect  the 
rise  of  the  conductor  over  the  sheath. 

2.  Resistivity  of  lead  12  times  that  of  copper.     This  assump- 
tion, while  not  strictly  correct,  will  give  results  within  an  accuracy 
obtained  by  considering  other  factors  as  constants,  such  as  the 
radiation  constants  of  the  lead  sheath. 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  85 

Definitions 

A  =  temperature  rise  of  conductor  over  sheath  for  a  given  con- 
ductor current. 

B  =  temperature  rise  of  sheath  over  cable  surroundings  for  the 
same  conductor  current  as  for  A . 

C  =  temperature  rise   of   conductor  over  cable  surroundings  for 
the  same  conductor  current  as  for  A  and  B. 

D  —  outer  diameter  of  lead  sheath  in  inches. 
d  =  inner  diameter  of  lead  sheath  in  inches. 

r  !       .     ,  area  in  circular  mils 

a  =  area  or  conductor  in  circular  inches  = • 

l,UUU,Uu(J 

Is  =  amperes  flowing  in  sheath. 

70  =  normal  current  rating  of  cable. 

X  =  defined  as  —• 

I'o 

I  =  conductor  current  with  (XI0)  sheath  currents. 

For  Single  Conductor  Cable 


12a 


For  Three  Conductor  Cables 


/=  T    _,,  4aX2  B 


(D*-d*)  (A  +  B) 
The  values  of  A,  B,  and  C  can  be  found  for  single  and  three 
conductor  cables  by  referring  to  Atkinson's  article  on  "Carrying 
Capacity  of  Cables"  in  the  September,  1920,  issue  of  the  Journal 
of  the  A.  I.  E.  E. 

Examples 

1.  Single  conductor  cable,  250,000  C.  M.,  1/8  inch  lead  sheath, 
4/32  inch  paper  insulation.  Normal  current  510  amperes.  What 
is  resultant  carrying  capacity  with  100  amperes  sheath  current? 


=        =  .  196,  X*  =  . 0384.     a  =  .250,  =  =  .735. 

olU  L>  Zo  .U 

D  =  1 .09,  d  =  .84,  D2  -  d?  =  .484. 


Resultant  carrying  capacity=510yi-  !!LMLL^ 
510  (.91)  =  463  amperes. 

2.  Round  Three  Conductor  No.  4/0,  paper  insulation, 


86  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

1/8  inch  lead  sheath.     Normal  current  242  amperes.     What  is 
resultant  carrying  capacity  with  200  amperes  sheath  current  ? 


D  =  2  .61,  d  =  2  .36,  D2  -  d2  =  1  .25. 

.,        0/lo    /,     4  (.2116)  (.684)  (.43) 
Resultant  carrying  capacity  =  242  -u  1  --  ^  -'  = 

.893  (242)  =  216  amperes. 

In  a  similar  way  the  reduction  of  current  carrying  capacity  for 
certain  cables  has  been  calculated  in  Tables  1  to  4.  Tables 
1,2,  and  3  are  for  single  conductor  cables  for  250  volt,  2,300  volt, 
and  600  volt  service,  respectively.  Table  4  is  for  13,200  volt, 
3  conductor  cables. 

The  normal  ampere  rating  in  the  second  column  of  Tables  1 
and  2  for  rubber  insulation  is  based  on  the  following  formula. 


Wherein  the  following  terms  are  used : 
di  =  diameter  of  copper  in  inches. 
dz  =  diameter  over  insulation  in  inches. 
dz  =  diameter  over  sheath  in  inches. 
K  =  resistivity  of  insulation  in  degrees  C.  rise  per  watt  per 

inch  cube. 

J  =  radiation  resistivity  of  lead  sheath  to  ambient  sur- 
roundings in  degrees  C.  rise  per  watt  per  inch  square. 
r  =  resistance  of  conductor  at  7\,  per  inch  length. 
/  =  current  carrying  capacity  of  cable. 
Tl  =  permissible  copper  temperature,  in  degrees  C. 
T2  =  temperature  of  ambient  surroundings  in  degrees  C. 
In  solving  the  formula,  the  following  values  of  the  several  con- 
stants were  taken :    . 

K  =  300°C.  rise  per  watt  per  inch  cube. 
J  =  200°C.  rise  per  watt  per  inch  square. 
T2  =  40°C. 

The  normal  ampere  rating  in  tables  3  and  4  for  paper  insula- 
tion is  based  on  the  data  in  the  paper  entitled  "High-Tension, 
Single-Conductor  Cable  for  Polyphase  Systems,"  by  W.  S. 
Clark  and  G.  B.  Shanklin,  Transactions  of  the  A.  I.  E.  E.,  1919, 
Vol.  XXXVIII,  page  917. 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 


87 


The  conductor  temperatures  used  are  in  practical  agreement 
with  Rule  9100,  page  95,  Revision  of  1921  of  the  Standards  of  the 
American  Institute  of  Electrical  Engineers. 

Where  different  normal  ampere  ratings  or  temperatures  are 
used,  the  percentages  of  normal  current  that  can  be  carried  with 
various  sheath  currents  will  differ  from  those  given  in  these  tables. 

Naturally,  the  effect  of  sheath  currents  is  greater  for  small  and 
medium  sized  cables,  and  it  may  be  noted  that  cables  of  these 
sizes  and  types  are  most  commonly  met  in  complicated  distribu- 
tion networks. 

Also,  for  the  same  size  conductor,  a  given  sheath  current  will 
reduce  the  current  carrying  capacity  of  the  cable  to  a  lesser  extent 
as  the  insulation  thickness  is  increased. 

In  cases  where  drainage  must  be  employed  and  where  heating 
is  a  factor,  the  sheath  currents  can  be  reduced  to  a  minimum  by 
limiting  the  drainage  to  the  smallest  values  which  will  protect  the 
system. 

TABLE   1. 

EFFECT  OF  SHEATH  CURRENTS  ON  ALLOWABLE  CONDUCTOR  CURRENT  OF 
SINGLE  CONDUCTOR  250-VOLT  2/32"  RUBBER  INSULATION.  SHEATH  AS- 
SUMED 1/16"  THICK. 


Conductor 
size 

Normal  ampere 
rating  at  60°  C. 
Conductor  temp. 
40°  ambient 

Per  cent  of  normal  rating  which  can  be  carried  with  sheath 
currents  as  indicated 

10  amp. 

20  amp. 

30  amp. 

40  amp. 

50  amp. 

No.  6.... 
4  
2  
1/0*.  . 

56 

75 
101 
137 

96.0 
96.8 
97.7 
98.3 

83.0 
86.6 
90.2 
93.0 

54.3 
66.0 
76.0 
83.0 

49!  5 
66.8 

37.2 

*  Thickness  insulation  =  5  /64' 


TABLE   2. 

EFFECT  OF  SHEATH  CURRENTS  ON  ALLOWABLE  CONDUCTOR  CURRENT  OF 
SINGLE  CONDUCTOR  2,300-VOLT  6/32"  RUBBER  INSULATION.  SHEATH  AS- 
SUMED 3/32"  THICK. 


Normal 

Conductor 

ampere 
rating  at 
60°C-.25E 

Per  cent  of  normal  rating  which  can  be  carried  with  sheath 
currents  as  indicated. 

size 

Conductor 

temp.  40° 

ambient. 

10  amp. 

20  amp. 

40  amp. 

50  amp. 

60  amp. 

70  amp. 

No.  6.... 

60 

99.2 

96.2 

90.9 

82.7 

71.9 

55.5 

23.5 

4  

79 

99.2 

96.5 

92.0 

85.3 

75.8 

62.2 

34.6 

2  

106 

99.3 

97.3 

93.7 

88.5 

81.0 

71.0 

57.1 

1/0  

139 

99.4 

97.6 

94.4 

89.5 

83.0 

74.3 

62.6 

88 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 


TABLE   3. 

EFFECT  OF  SHEATH  CURRENTS  ON  ALLOWABLE  CONDUCTOR  CURRENT  OF 
SINGLE  CONDUCTOR  600-VOLT  4/32"  PAPER  INSULATED  CABLES.  SHEATH 
ASSUMED  1/8"  THICK. 


Normal 

Per  cent  of  normal  rating  which  can  be  carried  with  sheath 

Conductor 

ampere 
rating  at 

currents  as  indicated. 

size 

85°C 

Conductor 

temp. 

50"  amp. 

75  amp. 

100  amp. 

125  amp. 

150  amp. 

175  amp. 

200  amp. 

250.000  c.m. 

510 

97.8 

96.4 

91.0 

85.5 

78.3 

68.7 

55.7 

500,000  c.m. 

720 

98.0 

95.7 

92.2 

87.5 

81.5 

73.6 

63.3 

750,000  c.m. 

880 

98.3 

96.3 

93.3 

89.4 

84.3 

77.8 

69.7 

1,000.000  c.m. 

1,010 

98.5 

96.7 

94.0 

90.3 

85.7 

80.0 

72.7 

1,500,000  c.m. 

1,250 

98.8 

97.2 

94.5 

91.8 

88.0 

83.3 

77.5 

2,000,000  c.m. 

1,440 

98.8 

97.3 

95.4 

92.7 

89.3 

85.0 

80.0 

TABLE   4. 

EFFECT  OF  SHEATH  CURRENTS  ON  ALLOWABLE  CONDUCTOR  CURRENT  OF 
ROUND  THREE  CONDUCTOR  13,200-VOLT  6/32  BY  6/32  PAPER  INSULATED 
CABLES  DUE  TO  STRAY  CURRENTS  FLOWING  ON  SHEATH.  SHEATH  AS- 
SUMED 1/8"  THICK. 


Conductor 
size 

Normal 
ampere 
rating  at 
75°  C. 
Conductor 
temp. 

Per  cent  of  normal  rating  which  can  be  carried  with  sheath 
currents  as  indicated 

50  amp. 

75  amp. 

100  amp. 

125  amp. 

150  amp. 

175  amp. 

200  amp. 

1/0  
2/0 

173 
193 
218 
242 
263 
290 
312 

99.3 
99.3 
99. 
99. 
99. 
99. 
99. 

98.4 
98.4 
98.5 
98.5 
98.6 
98.6 
98.7 

97.3 
97.2 
97.3 
97.5 
97.6 
97.8 
97.7 

95.6 
95.6 
95.5 
95.5 
96.2 
96.5 
96.4 

93.5 
93.5 
94.0 
94.0 
94.4 
95.0 
94.8 

91.2 
91.3 
91.8 
91.3 
92.3 
93.0 
93.0 

88.3 
88.4 
89.1 
89.3 
89.8 
90.7 
90.6 

3/0  

4/0  
250,000  c.m.. 
300.000  c.m.. 
350.000  c.m.. 

Good  duct  construction  with  vitrified  clay  or  fibre  conduit  for 
laterals  and  main  conduits,  and  the  draining  of  manholes  to 
sewers  or  by  sumps  will  tend  to  increase  the  resistance  of  the  cables 
to  earth,  and  thereby  reduce  the  tendency  to  collect  stray  currents. 
On  the  other  hand,  thorough  grounding  of  sheaths  is  in  many  cases 
resorted  to  as  a  protective  measure  for  isolated  sections. 

Where  it  is  impossible  to  protect  cable  systems  by  natural 
drainage,  boosters  have  occasionally  been  used  to  artificially 
lower  the  potential  of  the  cable  system.  This  practice,  as  well 
as  the  over  drainage  of  cable  systems,  is  objectionable  where 
other  underground  structures  are  involved  as  it  may  result  in 
unusually  high  potential  differences  between  the  piping  and 
cable  systems  with  resulting  damage  to  the  pipes. 
2.  Difference  Between  Cable  Drainage  and  Pipe  Drainage. 

The  early  use  of  drainage  as  a  method  of  affording  protection 
against  electrolysis  of  lead  covered  cables  led  to  the  proposal  to 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  89 

apply  the  same  method  of  protection  to  underground  piping 
systems.  The  result  is  that  more  or  less  pipe  drainage  has  been 
used,  particularly  on  water  systems  and  to  a  limited  extent  on 
gas  systems.  While  the  success  of  protecting  cable  systems  by 
drainage  is  generally  recognized,  there  are  important  differences 
in  the  application  of  drainage  to  cables  and  to  piping  systems 
which  make  the  application  of  drainage  to  the  latter  difficult 
and  uncertain.  Among  the  important  differences  between  the 
drainage  of  cable  and  piping  systems  are : 

1.  Cables  are  electrically  continuous  and  uniform  conductors, 
while  pipes  are  not  uniform  conductors  and  are  sometimes  dis- 
continuous conductors  due  to  the  joints  in  them.     Experience 
indicates  that  in  mains  having  cement  joints  a  large  percentage 
of  these  joints  are  of  high  resistance,  and  in  mains  having  lead 
joints,  occasional  joints  of  very  high  resistance  are  found  and 
many  of  the  joints  have  resistances  higher  than  several  lengths 
of  pipe.    -Therefore,  drainage  will  lower  the  potential  of  the  pipe 
for  relatively  short  distances  from  the  drainage  taps,  so  that  to 
be  effective  a  greater  number  of  drainage  taps  must  be  installed 
than  for  a  cable  system  of  the  same  extent.     The  number  and 
location  of  taps  will  depend  upon  the  extent  and  physical  layout 
of  the  pipe  network,  and  the  expense  involved  will  depend  upon 
the  number  and  locations  of  the  taps  required. 

2.  Under  certain  conditions  there  is  a  tendency  for  current 
flowing  on  a  pipe  to  leave  it  on  the  positive  side  of  a  high  resistance 
joint,  returning  to  the  joint  on  the  negative  side,  or  else  to  flow 
to  another  structure.     As  a  result  of  this,  joint  corrosion  may  occur 
at  high  resistance  joints  unless  both  sides  of  the  joint  are  main- 
tained negative  or  neutral  to  the  adjacent  earth  at  all  points  and 
under  all  conditions;   and   conversely,  no   electrolytic   corrosion 
will  occur  on  either  side  of  a  high  resistance  joint  if  the  entire 
surface  of  both  the  adjacent  pipe  lengths  is  permanently  negative 
to  the  surrounding  earth.     The  difficulty  of  keeping  a  complicated 
network  of  pipe  negative  to  the  adjacent  earth  by  means  of 
drainage  is  much  greater  than  in  the  case  of  cable  systems. 

3.  Cable  systems  are  placed  in  ducts  with  manholes  conveniently 
spaced  so  that  the  effect  of  the  application  of  drainage  to  a  cable 
system  may  be  adjusted  so  as  to  produce  the  results  desired, 
whereas  with  pipes  buried    in    the  ground,  and  in  large  cities 
beneath  improved  pavements,  it  is  more  difficult  to  make  the 
necessary  measurements  to  ascertain  the  effects  of  drainage. 

4.  Cables  are  relatively  small  and  contained  in  ducts  so  that 


90  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

unless  they  are  in  wet  or  marshy  ground,  they  are  but  partially 
in  contact  with  the  earth,  whereas,  gas  or  water  pipes  are  buried 
directly  in  the  earth.  Because  of  this  condition,  the  drainage  of 
an  underground  piping  system  with, but  few  high  resistance  joints 
results  in  the  flow  of  larger  amounts  of  current  than  does  the 
drainage  of  a  cable  system. 

5.  Currents  flowing  in  piping  systems  conveying  inflammable 
substances,  such  as  gas  or  oil,  constitute  a  fire  and  explosion 
hazard  and  many  cases  have  been  reported  where  stray  currents 
have  caused  arcs  which  have  ignited  the  gas  or  oil  when  the 
continuity  of  the  pipe  was  broken.  One  of  the  objections  to  the 
presence  of  excessive  currents  on  gas  or  oil  pipes  is  the  necessity 
for  bonding  around  a  cut  in  the  pipe  whenever  a  pipe  is  opened 
for  repairs.  Under  such  conditions  a  copper  wire  cable  is  con- 
nected around  the  point  on  the  pipe  to  be  opened.  Jumper 
cables,  terminating  with  adjustable  clamps  are  used  by  some 
companies  for  this  purpose. 

Under  certain  conditions  there  is  also  danger  of  increasing 
potential  differences  between  service  pipes  in  confined  air  spaces 
which  may  result  in  causing  arcs  due  to  the  intermittent  contact 
between  pipes  which  will  puncture  the  gas  pipes  and  ignite  the 
escaping  gas. 
3.  Application  of  Drainage  to  Pipes. 

(a)  Maintaining  Pipes    Negative  to  Earth.     Investigations  of 
the  Research  Subcommittee  show  that  when  electrical  drainage 
feeders  are  connected  to  a  jointed  piping  system  the  drained  pipe 
is  maintained  negative  to  the  soil  for  only  a  few  hundred  feet  from 
the  point  of  connection.     In  such  cases  it  is  necessary  to  extend 
the  drainage  feeder  along  the  principal  pipes  in  the  positive  area, 
which  extends  theoretically  about  40  per  cent  of  the  distance 
from  the  supply  station  to  the  end  of  the  feeding  district,  and 
connect  to  the  pipes  at  frequent  intervals. 

(b)  Effect  of  Pipe  Drainage  on  Current  Interchange.     Various 
conditions  exist  in  piping  systems  which  tend  to  affect  the  inter- 
change of  current  between  them,  and  these  should  be  fully  recog- 
nized in  the  consideration  or  employment  of  pipe  drainage. 

If  a  single  pipe  system  exists,  as  for  example,  a  water  system  in 
a  small  town,  the  drainage  of  that  system  will  not  as  a  rule  result 
in  objectionable  interchange  between  various  parts  of  the  network. 
However,  there  are  usually  several  piping  systems  present,  such 
as  a  lead  calked  water  pipe  system  and  a  lead  calked  gas  pipe  sys- 
tem. If  these  piping  systems  are  not  interconnected  at  many 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  91 

points  through  appliances,  or  are  not  otherwise  connected  together, 
the  drainage  of  one  or  both  systems  might  result  in  serious  inter- 
change of  current. 

The  application  of  drainage  to  one  piping  system  in  a  territory 
where  another  piping  system  exists  may  result  in  an  interchange 
of  current  between  the  drained  and  undrained  systems  so  it  is 
necessary  to  resort  to  the  common  drainage  of  all  of  the  piping 
systems  to  be  protected,  as  the  potential  inequalities  created  by 
separate  drainage  cause  electrolysis  at  points  where  the  current 
leaves  the  undrained  system  to  find  its  path  to  the  drained  system. 
Even  with  the  most  carefully  installed  and  maintained  unified 
system  of  drainage,  it  cannot  be  expected  that  all  danger  from 
current  interchange  will  be  eliminated. 

Pipe  systems  laid  with  cement  joints,  Dressser  Joints,  or  other 
high  resistance  joints  and  not  interconnected  with  other  systems, 
will  usually  need  no  other  form  of  protection  against  electrolysis. 
If,  however,  such  a  system  exists  in  a  territory  also  occupied  by  a 
piping  system  with  lead  calked  joints  and  connected  to  it  at  many 
points  through  applicances  or  otherwise,  the  service  pipes  of  the 
system  with  the  high  resistance  joints  and  the  sections  of  the  mains 
to  which  they  are  connected,  will  be  electrically  connected  to  the 
more  continuous  system  and  so  far  as  electrolysis  is  concerned 
should  be  considered  as  a  part  of  that  system.  Any  electrolysis 
condition  existing  on  the  continuous  system  will  therefore  be 
experienced  by  such  service  pipes  and  the  sections  of  the  mains 
of  the  discontinuous  system  as  connect  directly  with  it  and  any 
measure  which  tends  to  protect  the  continuous  piping  system  will 
also  affect  the  services  of  the  discontinuous  system.  This  con- 
dition is  illustrated  in  Fig.  18,  where  a  continuous  water  piping 
system  is  connected  through  appliances  to  gas  services.  Although 
the  gas  mains  are  laid  with  cement  joints,  they  are  being  damaged 
by  current  brought  to  them  over  the  water  mains. 

The  application  of  pipe  drainage  under  conditions  here  de- 
scribed may  afford  protection  to  some  portions  of  the  piping 
system  and  increase  the  damage  to  others.  In  some  areas  gas 
services  and  water  services  are  connected  with  each  other  through 
appliances  so  that  at  these  locations  the  two  piping  systems  are 
maintained  at  practically  the  same  potential.  In  most  piping 
networks,  however,  there  will  be  extensive  areas  where  the  gas  and 
water  systems  are  not  interconnected  by  such  appliances  and 
even  where  they  do  exist  they  cannot  always  be  relied  upon  to 
maintain  the  two  systems  at  practically  the  same  potential. 


92  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

(c)  Effects  of  Different  Kinds  of  Pipe  and  Joints.  A  fundamental 
difficulty  in  applying  electrical  drainage  to  piping  systems  is 
usually  present  and  this  is  the  great  variation  of  conductivity  of 
different  kinds  of  pipes  and  of  different  joints.  In  any  cast  iron 
piping  system  the  resistance  of  the  joints  varies  through  wide 
limits.  In  many  cities  there  are  a  number  of  different  kinds  of 
pipes  in  use:  steel  mains  with  welded  or  screw  joints  have  a  low 
resistance;  steel  mains  with  gaskets  made  of  rubber  are  high  in 
resistance,  while  cast  iron  mains  with  cement  joints  are  unusually 
high  in  resistance.  With  electrical  drainage  the  current  on  the 
pipes  is  increased  and  the  potential  drop  along  these  pipes  and 
over  the  joints  is  increased  in  like  proportions. 

Because  of  these  conditions  it  is  difficult  to  apply  drainage 
without  increasing  the  potential  differences  between  the  different 
piping  systems  at  some  points. 

SUMMARY  OF  GOOD  PRACTICE 

This  summary  is  intended  only  as  an  annotated  index  or  guide 
to  the  contents  of  Chapter  2  of  this  report,  not  as  a  substitute. 
Before  forming  an  opinion  or  taking  even  preliminary  action  on 
any  subject  treated  in  the  report  the  full  text  should  be  studied. 

A.  RAILWAYS 

1.  Track  Construction  and  Bonding.     (See  Page  25.) 

(a)  The  use  of  heavy  rails  with  joints  properly  bonded  and  well 
maintained  is  the  first  requirement  for  good  track  conductivity 
and  the  minimizing  of  stray  currents. 

(b)  In  paved  streets  welded  rail  joints  are  regarded  as  the  best 
and  most  permanent  form  of  bonding. 

(c)  Rail  joints  including  three  feet  of  rail  which  have  a  resistance 
in  excess  of  10  feet  of  adjacent  rail  should  be  rebonded,  except 
joints  bonded  with  long  bonds,  which  should  be  renewed  when 
the  resistance  exceeds  that  of  15  feet  of  adjacent  rail. 

(d)  Bonded  joints  should  be  tested  at  least  once  each  year  and 
such  tracks  as  show  bond  failures  in  excess  of  5  per  cent  annually 
should  be  tested  every  six  months.     A  failure  is  here  defined  as 
exceeding  the  resistance  specified  in  paragraph  (c). 

(e)  Cross  bonds,  connecting  the  two  rails  on  single  track,  and 
the  four  rails  on  double  track  should  be  installed  at  intervals  not 
to  exceed  500  feet  in  city  systems  and  from  1,000  to  2,000  feet  on 
interurban  lines. 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  93 

(f)  Jumpers  of  one  or  more  conductors  should  be  used  around 
all  special  work,  and  should  connect  to  all  rails  on  both  sides  of 
the  special  work.  The  size  of  such  jumpers  should  be  proportioned 
to  the  current  on  the  rails,  but  in  no  case  should  they  be  smaller 
than  No.  0000  for  one  track.  In  addition,  where  practicable,  all 
special  track  work  should  be  bonded  and  maintained  as  other 
track  rails. 

2.  Track  Insulation.     (See  Page  31.) 

(a)  In  the  construction  of  electric  railway  tracks  and  roadbeds 
the    electrolysis    problem    should   be    given    consideration   with 
economy  of  construction,  maintenance,  and  operation. 

(b)  Roadbeds  should  be  constructed  with  as  high  electrical 
resistance  to  earth  as  consistent  with  other  considerations,  special 
attention  being  given  to  keeping  them  dry  by  drainage.     Where 
practicable,  rails  should  be  kept  out  of  contact  with  the  earth. 

(c)  Clean  crushed  stone  ballast  offers  a  much  greater  electrical 
resistance  to  stray  current  than  does  solid  concrete  as  a  foundation 
under  ties. 

(d)  Where  crushed  stone  or  gravel  ballast  is  used  it  should  be 
kept  clean.     If  earth,  sand,  or  street  dirt  is  permitted  to  filter 
into  ballast  of  this  character  its  insulating  property  is  greatly 
impaired.     Vegetation  should  be  kept  down,  as  this  tends  to  make 
the  roadbed  moist  and  to  fill  the  ballast  with  foreign  material. 

(e)  Salts,  which  are  often  used  to  prevent  freezing  at  switches 
and  frogs,  greatly  reduce  the  resistance  of  roadbeds  and  should 
be  avoided  as  much  as  possible. 

(f)  Zinc  chloride  and  similar  chemical  tie  preservatives  reduce, 
while  creosote  and  gas  oil  increase  the  electrical  resistance  of  ties. 

3.  Reinforcement  of  Rail  Conductivity.     (See  Page  32.) 
Copper  is  not  economically  employed  when  connected  in  parallel 

with  tracks,  and  therefore  subjected  to  the  same  voltage  drop  as 
exists  on  the  tracks,  as  it  cannot  be  loaded  to  capacity  with  track 
voltage  drops  ordinarily  permissible. 

Buried  copper  conductors  or  old  rails  used  to  supplement  the 
track  return  also  increase  the  contact  area  between  the  return 
circuit  and  the  earth  and  thereby  tend  to  augment  stray  currents. 
For  these  reasons  the  use  of  such  supplementary  conductors 
should  be  avoided. 


94  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

4.  Power  Supply.     (See  Page  33.) 

(a)  Power  supply  stations  for  electric  railways  should  be  located 
with  consideration  to  their  effect  on  overall  potentials  and  potential 
gradients  in  the  tracks. 

(b)  In    selecting    locations    for    substations,    particularly    for 
interurban  lines,  consideration  should  be  given  to  the  extent  and 
character  of  the  underground*  metallic  structures  in  their  im- 
mediate vicinities. 

(c)  Connections  to  tracks  in  wet  locations  or  the  installation  of 
bare  track  feeders  in  earth  or  in  water  courses  should  be  avoided. 

(d)  Numerous  independent  connections  to  the  track  for  the 
return  of  current  aff<prd  the  most  effective  means  of  reducing  high 
potential   gradients  and  overall  voltages  and  thereby  limiting 
stray  currents,  and  as  many  should  be  provided  as  consistent  with 
good  engineering  and  economic  considerations. 

This  can  be  accomplished  by  the  use  of  additional  power  supply 
stations,  by  the  installation  of  insulated  negative  return  feeders, 
or  by  the  three-wire  system  wherein  each  car  on  the  negative 
trolley  becomes  a  point  of  return.  Combinations  of  these  may 
also  be  employed. 

(e)  The  most  generally  satisfactory  method  of  increasing  the 
number  of  independent  return  points  on  a  track  system  is  by  the 
use  of  additional  substations  and  the  tendency  of  railway  practice 
is  now  in  this  direction. 

(f)  Considerable  progress  has  been  made  in  recent  years  in  the 
development  of  automatic,  semi-automatic,  and  remote  control 
substations  and  these  are  now  being  used  both  on  interurban  lines 
and  for  city  service.     The  economies  attending  such  substations 
make  possible  a  greater  number  of  feeding  points  than  can  economi- 
cally be  supplied  through  manually  operated  stations. 

(g)  By  employing  the  maximum  number  of  substations  con- 
sistent with  economy,  rather  than  the  minimum  number,  stray 
currents  will  be  greatly  reduced. 

5.  Interconnection  of  Tracks.     (See  Page  47.) 

As  a  rule,  interconnection  of  tracks  will  improve  general  elec- 
trolysis conditions,  but  may  be  detrimental  in  one  locality  while 
improving  conditions  in  another. 

6.  Insulated  Negative  Feeder  System.     (See  Page  49.) 

(a)  Track  gradients  and  overall  potentials  can  be  limited  to 
any  desired  extent  by  the  use  of  insulated  negative  feeders  but 
the  cost  of  such  installations,  the  additional  power  loss  accompany- 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  95 

ing  their  use  and  the  reduction  in  operating  voltage  at  the  cars 
may  make  their  use  uneconomical  except  in  connection  with 
frequent  power  supply  stations. 

(b)  In  general  in  the  application  of  insulated  negative  feeders, 
the  negative  bus  should  be  connected  to  the  track  at  more  than  one 
point,  that  is,  negative  feeders  should  be  extended  along  the  track 
to  nearby  intersections.     Small  stations  of  300  to  500  kw.  capacity 
in  city  networks  may  usually  be  connected  directly  to  the  track 
at  one  point  only  and  preferably  to  the  nearest  track  intersection. 

(c)  Insulated  negative  feeders  should  be  run  from  the  negative 
bus  to  the  rails  in  such  a  manner  as  to  insulate  them  thoroughly 
from  the  earth  and  from  each  other.     The  tying  together  of  any 
of  these  feeders  should  be  avoided.     In  some  cases,  however,  it 
may  be  allowable  to  tie  a  single  feeder  to  the  rail  at  two  or  more 
points  through  resistances  to  adjust  the  currents  drawn  from  the 
tracks  at  the  various  points  of  connection. 

(d)  Connections  to  tracks  should  preferably  be  made  in  dry 
rather  than  in  wet  locations. 

(e)  Means  should  be  provided  on  all  negative  feeders  and 
feeder  taps  for  conveniently  measuring  the  current  flow  thereon 
and  where  practicable  these  means  should  be  installed  within  the 
power  supply  station. 

(f)  Insulated   negative   feeders   are   not   as   well   adapted   to 
reducing  stray  currents  from  interurban  lines  as  from  city  networks. 

7.  Three-Wire  System.     (See  Page  57.) 

(a)  The  three-wire  method  of  railway  power  supply  will  greatly 
reduce  stray  currents  when  properly  applied  and  also  give  better 
operating  voltage  at  the  cars. 

(b)  Where  a  few  large  supply  stations  are  used  the  first  cost  of 
converting  an  existing  railway  system  for  three-wire  operation 
is  usually  smaller  than  the  first  cost  of  any  other  measure  which 
will  give  the  same  degree  of  protection  from  electrolysis. 

(c)  There  are  difficulties  to  be  encountered  in  connection  with 
three-wire  operation  which  should  be  carefully  considered  before 
adopting  that  system. 

8.  Reversed  Polarity  Trolley  System.     (See  Page  62.) 

(a)  With  reversed  polarity  the  amount  of  stray  current  is  not 
reduced  but  the  electrolytic  corrosion  will  be  scattered  over  the 
outlying  districts  instead  of  being  confined  to  the  vicinity  of  the 
power  supply  station.  With  reversed  polarity  the  drainage  of 
cable  sheaths  is  rendered  impracticable. 


96  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

(b)  This  measure  should  not  be  considered  except  as  a  tem- 
porary means  of  relieving  dangerous  conditions  in  the  vicinity  of 
the  power  supply  station  at  the  expense  of  the  cables  and  piping 
systems  at  a  distance  from  the  station,  pending  the  installation 
of  an  effective  method  of  electrolysis  mitigation. 

9.  Periodic  Reversal  of  Trolley  Polarity.     (See  Page  63.) 

(a)  If  the  polarity  of  the  trolley  system  is  reversed  daily, 
electrolytic  corrosion  will  be  materially  reduced  although  the 
drainage  of  cable  sheaths  will  be  rendered  complicated  or  imprac- 
ticable. 

(b)  Some   of   the   difficulties   attending   three- wire   operation 
will  also  be  encountered  with  the  periodic  reversal  of  the  trolley. 

10.  Double  Contact  Conductor  Systems.     (See  Page  65.) 

(a)  Practically  complete  immunity  from  electrolysis  can  be 
had  by  the  use  of  a  properly  maintained  double  contact  conductor 
system  either  underground  or  overhead,  but  the  expense  and 
difficulties  involved  in  such  an  installation  are  not  justified  merely 
as  a  means  of  electrolysis  protection. 

11.  Alternating  Current  Systems.     (See  Page  46.) 

(a)  Electrolysis  resulting  from  the  use  pf  alternating  current 
by  street  railways  is  negligible. 

B.  AFFECTED  STRUCTURES 

1.  Location  with  Respect  to  Tracks.     (See  Page  66.) 

(a)  The  close  approach  of  piping  systems  to  railway  tracks  and 
the  laying  of  shallow  service  pipes  under  tracks  should  be  avoided 
as  far  as  practicable. 

(b)  On  streets  in  positive  areas  where  car  tracks  exist  gas  and 
water  mains  are  sometimes  installed  on  both  sides  of  the  streets. 
Such  construction  permits  the  use  of  shorter  services  and  obviates 
the  necessity  for  placing  service  pipes  under  tracks. 

2.  Avoidance  of  Contact  of  Cables  with  Pipes  and  Other  Struc- 

tures.    (See  Page  66.) 

(a)  In  the  installation  and  maintenance  of  cable  systems 
precautions  should  be  taken  to  avoid  contact  between  lead  sheaths 
and  other  underground  structures,  such  as  foreign  cables,  rails, 
steel  bridges,  gas  or  water  pipes  and  the  steel  frames  of  buildings, 
except  as  such  contacts  may  be  required  for  specific  reasons. 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  97 

3.  Conduit  Construction.     (See  Page  67.) 

(a)  Cable  sheaths  should  be  kept   out   of  intimate   contact 
with  the  earth  by  the  use  of  suitable  duct  materials,  proper  conduit 
construction,  and  Adequate  conduit  drainage.     Dips  in  the  conduit 
where  moisture  might  collect  should  be  avoided  wherever  prac- 
ticable. 

(b)  The  use  of  iron  pipe  for  laterals  to  poles  and  buildings 
should  be  confined  to  conditions  where  no  other  form  of  conduit 
is  suitable  or  permissible. 

(c)  Wherever  long  laterals  to  poles  are  installed  the  horizontal 
portion  should  be  of  vitrified  tile,  fiber,  stone  or  some  similar 
duct  material,  using  iron  pipe  only  for  the  bend  at  the  base  of 
the  pole  and  for  the  vertical  portion  up  the  pole. 

(d)  Unless   necessary   as    a    protective   measure   for   isolated 
sections,    cable    sheaths    should    not    be    artificially    grounded. 
Grounds  in  negative  areas  through  which  stray  current  might  be 
picked  up  should  be  avoided  whenever  practicable. 

4.  Insulating  Joints  in  Cable  Sheaths.     (See  Page  70.) 

(a)  Insulating  joints  are  sometimes  used  in  cable  sheaths 
under  special  conditions  to  prevent  electrolytic  injury  which 
might  result  from  contact  with  steel  bridges  or  buildings.  They 
are  also  occasionally  used  to  prevent  the  flow  of  current  on  cable 
sheaths  where  drainage  is  undesirable  or  impracticable. 

5.  Surface  Insulation  of  Pipes  and  Cables.     (See  Page  71.) 

(a)  Surface  insulation  in  the  form  of  dips,  paints,  and  wrappings 
cannot  be  depended  upon  as  a  permanent  method  of  preventing 
electrolysis. 

(b)  Thick  coatings  in  the  form  of  pitch  or  parolite  poured 
into  a  containing  box  built  around  the  pipe  are  occasionally  used 
in   preventing   electrolysis  under  special   conditions  where   the 
expense  is  warranted. 

6.  Insulating  Joints  in  Pipes.     (See  Page  74.) 

(a)  Insulating  or  high  resistance  joints,  such  as  those  of  the 
Dresser  type  or  cement  joints,  if  used  throughout  a  pipe  line  at 
frequent  intervals,  or  at  specially  selected  locations  may  afford 
substantial  protection  against  electrolysis.     This  practice  relates 
particularly  to  gas  and  oil  pipes. 

(b)  It  is  sometimes  permissible  to  use  a  comparatively  few 
insulating  joints  if  care  is  taken  to  see  that  the  flow  of  current 
on  the  pipe  is  practically  eliminated. 


98  DESIGN,  CONSTRUCTION,  OPERATION,  ETC. 

(c)  Insulating  joints  are  often  installed  in  service  pipes  for  the 
purpose  of  preventing  the  interchange  of  current  between  pipe 
systems. 

7.  Shielding.     (See  Page  79.)  * 

In  special  locations  a  pipe  may  be  protected  from  electrolysis 
by  a  metal  shield,  wholly  or  partly  surrounding  it  and  electrically 
connected  thereto. 

C.  INTERCONNECTION  OF  AFFECTED  STRUCTURES  AND 
RAILWAY  RETURN  CIRCUIT 

1.  Cable  Drainage.     (See  Pages  81  and  83.) 

(a)  Lead  sheath  cables  in  urban  districts  or  where  parallel 
with  interurban  railways  commonly  require  some  form  of  elec- 
trolysis protection  and  this  is  usually  accomplished  by  drainage. 

(b)  In  some  cases  the  heating  effect  of  stray  current  on  the 
sheaths  of  power  cables  may  reduce  the  current  carrying  capacity 
of  the  cable. 

(c)  Drainage  connections  should  be  made  to  the  negative  bus 
of  the  railway  supply  station  or  to  the  rail  terminal  of  insulated 
negative  feeders.     Connections  to  the  rails  should  in  general  be 
avoided. 

(d)  Cable  sheaths  when  drained  are  made  negative  to  the 
surrounding  earth  at  practically  all  times.     Drainage  should  be 
reduced  to  a  minimum  consistent  with  the  protection  of  the 
cables. 

(e)  In  general,  all  signal  cable  sheaths  in  any  conduit  system 
should  be  bonded  together  at  every  man  hole.     Where  advisable 
and   permissible   all   power   cable   sheaths   should   be   similarly 
bonded. 

(f)  So  far  as  practicable  or  advisable,  all  cable  systems  should 
be  drained  at  the  same  locations  or  by  the  same  drainage  feeders 
and  differences  of  potential  between  adjacent  or  intersecting  cable 
systems  should  be  eliminated  by  cross  bonding. 

(g)  Fuses  should  be  installed  in  all  connections  between  signal 
and  power  cable  sheaths,  and  should  be  so  proportioned  as  to 
protect  the  sheaths  from  dangerous  currents. 

(h)  Means  should  be  provided  for  conveniently  measuring  all 
drainage  currents  and  maintaining  close  supervision  on  all  drainage 
systems,  and  where  possible  this  should  be  accomplished  by  in- 
stalling meters  within  the  power  supply  station  and  making  them 
accessible  to  the  cable  owning  companies. 


DESIGN,  CONSTRUCTION,  OPERATION,  ETC.  99 

(i)  Means  and  operating  regulations  should  be  provided  for 
opening  all  drainage  cables  during  periods  when  reverse  currents 
would  otherwise  flow  over  them,  if  the  magnitude  and  duration 
of  such  reverse  currents  is  objectionable. 

2.  Pipe  Drainage.     (See  Pages  88  to  91.) 

(a)  There  are  wide  differences  of  opinion  among  competent 
engineers  who  have  studied  pipe  drainage,  as  to  its  adaptability 
to    various    conditions.     Numerous    questions    are    involved   in 
regard  to  which  there  is  not  sufficient  information  available  at 
the  present  time  to  permit  the  drawing  of  accurate  conclusions, 
and  for  this  reason  this  subject  is  being  investigated  by  the 
Research  Sub-Committee  of  the  American  Committee  on  Elec- 
trolysis.    There  are,  however,  certain  objections  to  the  use  of 
pipe  drainage  which  are  discussed  in  this  report  and  which  should 
be  carefully  considered  before  employing  it. 

(b)  Pipe  drainage  is  in  use  more  or  less  on  water  systems  and 
to  a  limited  extent  on  gas  systems. 

(c)  As  a  method  of  mitigation,  drainage  is  not  so  well  adapted 
to  pipes  as  to  cable  sheaths. 

(d)  High  resistance  joints  are  prevalent  in  all  jointed  pipe  lines 
and  they  greatly  complicate  the  application  of  drainage. 

(e)  To  lower  the  potential  of  a  jointed  piping  system  below 
that  of  the  surrounding  earth,  it  is  usually  necessary  to  extend 
the  drainage  conductors  over  a  considerable  area  and  connect 
to  the  pipes  at  numerous  locations. 

(f)  Corrosion  at  high  resistance  joints  in  pipe  lines  carrying 
current  may  occur  unless  the  pipe  on  both  sides  of  the  joint  is 
maintained  negative  or  neutral  to  the  adjacent  earth,  in  which 
case  no  corrosion  will  occur. 

(g)  Drainage  generally  increases   the   current  flow  on  pipes 
and  such  current  increases  the  hazard  from  oil  and  gas  ignitions 
and  explosions. 

(h)  In  small  towns  on  interurban  railways  pipe  drainage  is 
less  objectionable  than  in  urban  districts  where  complicated  pipe 
networks  exist. 

(i)  Drainage  of  a  large  network  of  pipes  should  be  used  only 
as  an  auxiliary  to  a  railway  system,  properly  designed  and  main- 
tained from  the  electrolysis  standpoint.  When  so  used  it  should 
be  installed  and  maintained  under  competent  supervision. 


CHAPTER  3 
ELECTROLYSIS  SURVEYS 

I.  INTRODUCTION 
A.  PURPOSE  AND   SCOPE  OF  ELECTROLYSIS  SURVEYS 

1.  Purpose  of  Electrolysis  Survey.* 

Electrolysis  surveys  deal  with  the  various  methods  and  classes 
of  measurement  employed  to  determine  the  hazard  to  underground 
metallic  structures  due  to  stray  electric  currents,  the  extent  of 
existing  damage  already  produced,  and  the  mitigative  measures 
that  may  best  be  employed  for  reducing  the  danger  of  future 
trouble.  There  are  discussed  below  the  methods  of  determining 
electrolysis  conditions,  of  collecting  data  upon  which  the  design 
of  mitigating  systems  may  be  based,  the  types  and  kinds  of 
instruments  that  should  be  used,  the  procedure  to  be  followed  in 
the  working  up  of  the  data,  and  the  interpretation  of  the  results 
of  the  survey. 

2.  Difficulty  of  Standardizing  Survey  Procedure. 

It  should  be  emphasized  that  in  general,  no  two  electrolysis 
surveys  will  be  conducted  in  precisely  the  same  manner,  so  that 
specific  rules  of  procedure  cannot  be  laid  down  that  will  be  appli- 
cable to  all  cases.  The  procedure  set  forth  below  is  intended  to 
cover  the  measurements  that  experience  has  shown  are  most 
frequently  required,  and  to  describe  the  best  methods  of  taking 
such  measurements.  The  number  of  readings  taken  and  the 
procedure  to  be  followed  will  vary  so  much  with  local  conditions 
that  reliance  must  be  placed  on  the  judgment  of  the  person  making 
the  test.  In  fact,  the  proper  procedure  during  a  large  part  of  the 
survey  will  depend  in  large  measure  on  the  results  obtained  in 
preliminary  tests.  It  is  important,  therefore,  that  electrolysis 
investigations  of  any  importance  be  made  under  the  direction  of 
a  competent  engineer  very  familiar  with  methods  of  procedure 
and  the  interpretation  of  electrolysis  test  data. 

3.  Information  Obtainable  by  Electrolysis  Surveys. 

By  means  of  proper  measurements,  it  is  possible  to  determine 

with  a  fair  degree  of  defmiteness,  the  extent  and  location  of  the 

% 

*For  a  definition  of  the  term  electrolysis  survey  and  other  terms  used  in  this 
chapter,  see  Chapter  1,  on  Principles  and  Definitions. 
100 


ELECTROLYSIS"  $AVS'<  -'•     101 

areas  in  which  pipes  and  other  structures  are  endangered  by 
stray  currents  and,  with  sufficient  accuracy  for  most  purposes, 
the  degree  of  seriousness  of  the  trouble.  The  cause  of  any  damage 
that  may  be  in  progress  at  the  time  of  the  survey,  whether  due  to 
stray  currents  or  corrosion  by  the  soil,  cinders,  or  other  natural 
causes,  can  generally  be  ascertained,  and  in  the  case  of  stray 
current  corrosion,  the  source  of  the  current  can  generally  be  deter- 
mined. The  various  factors  connected  with  pipe  systems,  such 
as  high  resistance  joints,  very  low  soil  resistances,  and  the  use  of 
improper  mitigative  measures,  can  also  be  detected.  Defects 
in  the  railway  return  system,  such  as  poorly  bonded  rail  joints, 
infrequent  cross  bonds,  insufficient  conductance  in  the  negative 
return,  improper  use  of  such  conductance,  excessive  feeding 
distances  and  other  causes  of  electrolysis  trouble  can  usually  be 

definitely  determined. 

• 

B.  TYPES  OF  SURVEYS 

In  the  following  discussion  several  types  of  surveys  must  be 
recognized.  The  first  is  that  which  may  be  called  a  complete 
electrolysis  survey  which  is  made  for  the  purpose  of  determining 
the  extent  and  location  of  the  danger  areas,  and  with  a  view  of 
determining  the  proper  procedure  to  be  followed  for  the  mitiga- 
tion of  any  trouble  which  may  be  found  to  exist 

The  second  type  of  survey,  known  as  a  maintenance  survey, 
embraces  such  surveys  as  would  usually  be  made  by  a  pipe  or 
cable  owning  company,  solely  for  the  purpose  of  determining 
whether  previously  existing  conditions  have  changed  and  differs 
from  the  more  complete  survey  mainly  in  that  most  of  the  in- 
formation with  respect  to  the  railway  power  distribution  system 
is  not  required  and  fewer  electrical  measurements  are  taken,  the 
number  and  character  of  such  measurements  depending  on  the 
thoroughness  with  which  the  survey  is  to  be  carried  out. 

A  third  type  of  survey  which  needs  little  discussion,  except  as 
to  methods  of  making  tests,  is  one  made  to  determine  whether 
ordinances  or  regulations  governing  electrolysis  conditions  in  a 
municipality  are  being  complied  with.  Such  surveys  are  usually 
made  periodically,  in  periods  varying  from  three  months  to  a  year. 
In  general,  only  those  quantities  are  measured  which  are  speci- 
fically defined  by  the  ordinances  or  regulations  which  are  in 
effect  in  the  locality  in  question. 


102  riMCTROLYSIS  SURVEYS 

C.  GENERAL  PRELIMINARY  DATA 

1.  Data  on  Underground  Structures. 

In  making  electrolysis  surveys,  a  considerable  amount  of 
preliminary  data  are  usually  desirable.  It  is  important  first  to 
gather  all  evidence  regarding  the  character,  extent  and  location 
of  known  damage  to  underground  structures.  This  evidence  is 
usually  obtained  from  the  utility  companies  concerned,  but  even 
though  these  companies  can  give  no  direct  testimony  as  to  the 
injury  to  underground  structures,  this  should  not  be  taken  to 
indicate  that  no  damage  exists.  The  data  on  the  underground 
systems  should  include  the  relative  location  of  the  mains,  the  rail- 
way tracks  and  underground  cable  systems.  The  size  and  kinds 
of  pipe  and  the  types  of  pipe  joints  used  are  usually  important. 
Numerous  questions  relating  to  the  interconnection  of  gas,  water, 
and  cable  systems  are  also  of  importance. 

2.  Data  on  Railway  Systems. 

As  regards  the  data  on  the  railway  systems,  the  following 
should  be  determined:  (1)  Location  and  capacities  of  direct 
current  railway  supply  stations :  (2)  Location  of  railway  lines  and 
character  of  service,  whether  city,  suburban,  or  interurban  and 
the  car  schedules  on  different  parts  of  the  system.  This  latter 
will  have  a  bearing  on  the  length  of  time  necessary  for  taking 
readings  at  various  points  in  order  to  get  representative  results; 
(3)  Physical  data  on  railway  tracks,  such  as  size  of  rails,  types  of 
bonds  and  joints,  and  character  of  roadbed  construction;  (4) 
Practice  of  the  railway  company  in  regard  to  crossbonding, 
bond  maintenance  and  bond  testing;  and  (5)  Miscellaneous  data. 
In  most  cases  it  is  desirable  to  have  all-day  load  curves  to  facilitate 
the  interpretation  of  data  taken  over  short  intervals  at  various 
hours  of  the  day.  Where  the  load  varies  considerably  in  different 
sections  of  a  power  house  feeding  area,  it  may  be  necessary  to 
get  the  load  curve  on  different  feeders  in  some  cases.  Where  a 
survey  is  made  with  the  ultimate  purpose  of  correcting  electrolysis 
conditions  by  applying  some  method  of  mitigation,  it  will  be 
necessary  to  secure  complete  data  on  the  magnitude  and  distribu- 
tion of  the  load,  the  substation  and  feeder  systems,  frequency  of 
schedules  and  probable  future  growth  of  traffic. 

D.  COOPERATION  IN  MAKING  SURVEYS 

Special  surveys  for  determining  whether  ordinances  are  being 
complied  with  and  maintenance  surveys  can  usually  be  made 
by  any  particular  utility  interested.  Complete  surveys,  however, 


ELECTROLYSIS  SURVEYS  103 

which  are  to  be  preliminary  to  the  application  of  electrolysis 
mitigative  measures  should  preferably  be  carried  out  on  a  coopera- 
tive basis  by  the  various  utilities  interested,  including  both  the 
railways  and  owners  of  underground  utilities.  It  is  of  the  utmost 
importance  that  a  comprehensive  plan  of  procedure  be  followed, 
so  that  all  information  relating  to  the  electrolysis  conditions  of 
all  of  the  underground  structures  may  be  available  in  the  planning 
and  carrying  out  of  the  test.  In  order  to  bring  about  such  a 
unification  of  data  and  methods,  it  is  necessary  to  have  the  full 
cooperation  of  all  utilities  whose  properties  are  affected  by  elec- 
trolytic conditions.  In  general,  this  cooperation  can  best  be 
brought  about  by  having  the  electrolysis  survey  and  the  mitiga- 
tive measures,  if  any  are  to  be  applied,  designed  and  installed 
under  the  jurisdiction  of  a  joint  committee  representing  all  of  the 
interests  concerned  or  at  the  discretion  of  such  committee  by  an 
engineer  employed  by  the  committee,  or  jointly  by  the  parties  to 
the  survey. 

II.  ELECTRICAL  MEASUREMENTS 

The  electrical  measurements  to  be  made  during  an  electrolysis 
survey  may  be  logically  classified  in  either  of  two  ways,  namely, 
(1)  on  the  basis  of  the  structures  on  which  the  measurements  are 
to  be  made,  that  is,  whether  on  the  railway  system,  pipe  system, 
or  cable  system,  and  (2)  on  the  basis  of  the  character  of  the 
measurements,  whether  of  voltage,  current  on,  or  current  leaving 
a  structure,  etc.  Inasmuch  as  several  or  all  of  the  various  types 
of  electrical  measurements  may  at  times  have  to  be  made  on  all 
of  the  affected  structures,  and  since  the  methods  used  will  be  sub- 
stantially the  same  regardless  of  the  utility  system  to  which  they 
apply,  it  appears  most  logical  to  follow  the  latter  classification 
and  discuss  the  subject  from  the  standpoint  of  the  character  of  the 
measurements  to  be  made. 

A.  VOLTAGE  SURVEYS 

The  number  and  character  of  the  potential  readings  required 
depend  on  the  information  desired.  As  previously  pointed 
out,  the  readings  depend  on  the  thoroughness  of  the  investigation 
to  be  made,  and  it  is  to  be  understood  that  many  of  the  measure- 
ments described  below  would  often  not  be  necessary,  and  in 
general  would  be  taken  only  during  the  course  of  a  complete 
electrolysis  survey.  Voltage  surveys  are  here  divided  into  two 
main  classes:  (a)  Voltage  measurements  between  two  points  on 


104  ELECTROLYSIS  SURVEYS 

the  same  structure,  and  (b)  Measurement  of  the  potential  differ- 
ence between  structures. 

1.  Measurement  of  Maximum  Potential   Drop   Along   Railway 
Structures. 

(a)  Importance   of  Maximum    Potential    Drop   Measurements. 
Such  measurements,  when  interpreted  in  the  light  of  other  con- 
ditions to  be  discussed  later,  afford  a  valuable  index  to  electrolysis 
conditions  generally.     It  is,  further,  one  of  the  easiest  quantities 
to  determine  in  an  electrolysis  survey  if  the  use  of  telephone  lines 
can  be  secured.     These  measurements  show  in  general  whether 
the  railway  system  is  properly  'maintained  and  what  lines  or  sec- 
tions are  most  in  need  of  repair  and  rebonding.     When  taken  in 
conjunction  with  the  load  data,  they  may  be  used  for  an  approxi- 
mate calculation  of  power  losses  in  the  railway  return  and  when 
studied  with  due  regard  to  the  character  and  location  of  railway 
lines  and  supply  stations,  together  with  the  distribution  of  load, 
they  afford  a  valuable  index  as  to  the  need  of,  or  the  modification 
of  the  track  feeder  system.     It  is  therefore  desirable,  as  a  rule, 
to  take  a  good  many  of  these  measurements  as  a  part  of  any 
complete  electrolysis  survey. 

(b)  Procedure  in  Making  Maximum  Potential  Drop  Measure- 
ments.    The  first   step  in  making  measurements  of  this  kind 
in  a  city  is  to  determine  the  location  of  points  between  which 
potentials  are  to  be  observed.     These  usually  comprise  points  on 
the  track  most  remote  from  the  power  supply  station  as  the 
points  of  highest  potential,  and  the  points  on  the  track  nearest 
the  power  station  as  the  point  of  lowest  potential.     In  some  cases, 
however,  especially  where  insulated  track  feeders  are  used,  the 
point  of  lowest  potential  may  be  at  the  point  of  connection  of 
one  of  the  insulated  feeders  which  may  be  at  a  considerable 
distance  from  the  power  station.     It  is  desirable,  as  a  rule,  to 
measure  the  difference  of  potential  between  the  points  of  connec- 
tion to  the  tracks  of  all  of  the  insulated  track  feeders  in  order 
that  the  points  of  lowest  potential  may  be  determined.     It  is 
desirable,  as  a  rule,  also  to  select  points  intermediate  between  the 
points  of  highest  and  lowest  potential  so  that  the  distribution  of 
the  potential  drop  may  be  determined,  as  this  will  give  a  valuable 
insight  into  the  location  of  bad  stretches  of  track  and  of  concen- 
tration of  return  current  in  the  tracks. 

Reference  should  be  made  to  a  positive  feeder  map  from  which 
a  list  of  power  stations  and  their  approximate  feeding  distances 
can  be  determined.  Special  lines  to  these  points  may  be  run  or 


ELECTROLYSIS  SURVEYS  105 

spare  wires  may  be  borrowed  or  leased  from  the  telephone  company. 
In  the  latter  case,  the  continuous  cooperation  of  the  telephone 
company  is  required.  Having  a  list  of  points  to  be  reached,  the 
telephone  representatives  can  prepare  a  table  showing  the  ter- 
minal boxes  and  numbers  of  spare  pairs,  including  trunk  lines 
which  are  necessary  to  make  a  complete  circuit  between  one  of  the 
telephone  central  offices,  or  other  suitable  central  point  where 
the  measuring  instruments  are  to  be  placed  and  the  points  to  which 
measurements  are  to  be  made.  All  measurements  can  then  be 
made  between  the  point  of  lowest  potential  and  all  other  points 
selected,  and  between  any  two  points  as  desired.  Temporary 
circuits  are  necessary  when  no  spare  telephone  conductors  are 
available,  in  which  case  working  conductors  may  sometimes  be 
used  for  short  periods.  In  most  cases,  it  is  desirable  to  make 
permanent  connections  to  the  track  for  maximum  voltage  drop 
measurements,  but  where  for  any  reason,  permanent  or  semi- 
permanent connections  to  the  track  cannot  be  made,  temporary 
connections  become  necessary  and  the  installation  of  these  tem- 
porary connections  will  require  considerable  time  and  expense 
for  labor. 

It  will  be  found  most  convenient  to  bring  all  the  lines  from  the 
various  points  on  the  track  network  to  a  large  board  on  which  is 
mounted  a  map  of  the  railway  system,  each  wire  being  fastened 
to  a  binding  post  located  at  a  point  on  the  map  corresponding  to 
the  point  on  the  track  from  which  the  wire  comes.  Once  the 
correct  connection  of  wires  has  been  verified,  one  can  readily 
connect  the  voltmeter  to  wires  leading  to  any  points  in  the  city 
without  possibility  of  error. 

While  making  track  voltage  measurements,  and  in  fact,  all 
other  measurements,  it  is  desirable  to  arrange  to  have  the  test 
data  worked  up  and  tabulated  so  that  it  can  be  carefully  studied 
as  the  work  progresses.  This  is  important  because,  as  pointed 
out  above,  the  tests  to  be  made  during  the  course  of  the  survey 
often  depend  in  large  measure  on  the  results  of  preliminary 
measurements  so  that  by  .making  a  study  of  the  preliminary  data 
while  the  work  is  in  progress,  it  is  often  possible  to  modify  original 
plans  in  such  a  way  as  to  greatly  increase  the  value  of  the  test 
data. 

In  making  electrolysis  measurements,  it  is  desirable  to  take 
readings  at  each  point  over  as  long  a  period  as  practicable.  Owing 
to  the  great  variability  of  railway  loads,  it  is  important  to  have 
the  readings  cover  at  least  one  complete  cycle  of  the  load,  and 


106  ELECTROLYSIS  SURVEYS 

often  several  complete  cycles  are  desirable.  It  is  quite  common 
practice  to  take  such  readings  over  a  period  of  one  hour,  but  in 
some  cases,  especially  on  interurban  lines  and  others  where  the 
schedule  is  very  infrequent,  still  longer  periods  may  be  necessary. 
Even  where  readings  are  taken  over  one  hour  it  will  generally 
be  necessary  for  comparative  purposes  to  reduce  these  readings 
to  an  equivalent  twenty-four-hour  value,  and  in  some  cases  also 
corrections  have  to  be  made  for  seasonal  changes  of  the  load. 
This  matter  will  be  treated  at  some  length  under  the  discussion 
of  the  interpretation  of  electrolysis  survey  data. 

2.  Potential  Gradient  Measurements. 

(a)  Scope  of  Term.     Under  the  head  of  potential    gradients 
will  be  included  all  potential  measurements  between  different 
points  on  the  track  or  between  different  points  in  the  earth  spaced 
materially  less  than  the  extreme  feeding  distances  within  the 
powerhouse  areas. 

(b)  Measurement  of  Potential  Gradients  in  Tracks.     Potential 
gradient  measurements  are  usually  made  on  the  railway  tracks, 
but  at  times  also  on  pipe  systems  or  even  in  the  earth.     The 
procedure  will  vary  considerably  because  of  the  variability  of  the 
distances   over  which  measurements  are  to  be  made.     If  the 
spans  are  long,  telephone  wires  are  the  most  convenient  and  the 
measurements  are  made  in  the  same  way  as  track  voltage  measure- 
ments   described    above.     Where    the    distances    are    relatively 
short,  however,  as  for  example,  a  few  hundred  feet  or  less,  a 
temporary  wire  between   the  two  points  of  measurement  will 
usually  be  most  convenient.     Connections  to  the  system  on  which 
measurements  are  made  will  depend  on  whether  the  tests  are  being 
made  between  points  on  the  tracks  or  on  the  pipe  system  or 
between  points  in  the  earth.     For  measurements  between  points 
on  the  tracks  or  on  the  pipe  system  or  other  metallic  structure 
metallic  terminals  may  be  firmly  held  against  the  rail  or  pipe 
or  a  wire  may  be  swedged  in  a  slot  sawed  in  the  pipe  or  rail  under 
test.     It  is  sometimes  desirable  to  make  potential  measurements 
directly  between  two  points  in  the  earth,  though  the  most  common 
practice  has  been  to  take  them  on  the  track  network.     Special 
situations    may    arise   where    potential   measurements    between 
various  points  in  the  earth  are  more  valuable  than  those  taken 
on  the  underground  structures.     For  example,  the  presence  and 
direction  of  large  transverse  currents  in  the  vicinity  of  important 
mains  can  be  determined.     Buried  pipe  lines  or  other  conductors 


ELECTROLYSIS  SURVEYS  107 

at  uncertain  locations  which  are  discharging  current  into  the 
earth  may  be  located  approximately  by  earth  gradient  measure- 
ments, there  being  a  reversal  or  abrupt  change  in  the  gradient 
when  the  conductor  is  crossed. 

In  making  earth  gradient  measurements  between  points  rel- 
atively close  together,  it  is  essential  that  a  pair  of  non-polarizable 
electrodes  be  used  if  a  high  degree  of  accuracy  is  to  be  attained. 
Such  electrodes  are  now  in  process  of  development  at  the  Bureau 
of  Standards. 

The  periods  over  which  gradient  measurements  should  be  made 
and  the  procedure  in  working  up  the  data  during  the  progress 
of  the  survey  are  governed  by  the  same  considerations  as  dis- 
cussed above  in  the  treatment  of  the  track  voltage  measurements. 

3.  Measurement  of  Potential  Differences. 

(a)  Purpose  of  Measurement  of  Potential  Differences.     Measure- 
ment of  potential  differences  are  beyond  question  the  measure- 
ments  most   frequently   made   in    connection   with    electrolysis 
tests  and  when  their  limitations  are  properly  taken  into  account, 
they  afford  a  valuable  index  to  electrolysis  conditions.     It  should 
be  emphasized,  however,  that  they  are  chiefly  of  qualitative  sig- 
nificance, being  valuable  for  indicating  the  region  in  which  more 
or  less  damage  to  pipes  may  be  in  progress,  but  not  giving  any 
definite  information  as  to  the  rate  at  which  injury  to  pipes  may 
be  progressing.     This  is  due  to  the  fact  that  the  resistivity  of  the 
earth  and  railway  roadbed  varies  with  local  conditions,  that  is, 
a  given  potential  difference  that  would  be  practically  safe  under 
some  conditions  of  soil  resistance  would  be  extremely  hazardous 
in  other  locations.     If  this  factor  is  properly  taken  into  account, 
potential  difference  measurements  may  be  of  considerable  value 
in  determining  electrolysis  conditions. 

(b)  Procedure  in  Making  Measurements  of  Potential  Differences. 
Measurements  of  potential  differences  between  adjacent  structures 
should  be  made  at  many  points  between  fire  hydrants,  lamp  posts 
or  gas  or  water  services  and  tracks,  lead  cable  sheaths  and  tracks, 
lead  cables  and  accessible  portions  of  pipe  systems,  between  any 
two  pipe  systems  that  approach  closely  to  each  other,  and  where 
practicable  between  cable  systems  and  the  earth.     In  making 
contacts  on  fire  hydrants  and  lamp  posts,  care  should  be  taken  to 
make  contact  with  the  pipe  itself,  rather  than  the  housing.     These 
measurements,    between   cable   systems   and  earth,   if  properly 
taken,  afford  the  most  valuable  index  of  electrolysis  conditions, 
but  unfortunately,  they  are  the  most  difficult  to  secure,  and 


108  ELECTROLYSIS  SURVEYS 

unless  taken  by  a  competent  engineer,  thoroughly  familiar  with 
the  possible  sources  of  error  involved,  they  may  be  worthless  or 
actually  misleading.  These  measurements  when  taken  should 
be  made  throughout  a  large  part  of  the  piping  or  cable  networks 
including  any  regions  in  which  there  is  reason  to  believe  that 
stray  current  may  be  leaving  the  affected  structures  for  the 
earth. 

Since  the  structures  between  which  potential  difference  measure- 
ments are  made  are  usually  close  together,  short  leads  only  are 
required,  short  lengths  of  lamp  cord  or  other  flexible  wire  being 
most  commonly  used.  Either  temporary  or  more  or  less  per- 
manent connections  to  metallic  structures  may  be  made,  accord- 
ing to  whether  readings  are  to  be  taken  over  a  short  or  long  period 
and  whether  they  are  to  be  repeated  at  some  future  time.  When 
measuring  potential  differences  between  pipe  or  cable  systems 
and  the  earth,  it  is  important  to  use  an  auxiliary  earth  electrode 
that  is  known  to  give  a  very  small  galvanic  potential  against  the 
metal  of  the  structure  under  test.  For  lead  cables  a  piece  of 
ead  sheath  is  entirely  satisfactory.  In  the  case  of  iron  pipes  thel 
problem  is  more  difficult  because  of  the  variability  of  iron  and 
the  possibility  of  complication  due  to  oxidation  of  either  the  pipe 
under  test  or  the  auxiliary  iron  electrode.  When  such  readings 
with  iron  electrodes  amount  to  only  a  few  tenths  of  a  volt  they 
should  not  be  regarded  as  reliable  unless  taken  over  a  period  in- 
cluding that  during  which  the  railway  power  station  is  shut  down, 
owing  to  the  possibility  of  galvanic  voltages  being  of  this  order 
of  magnitude. 

B.  CURRENT  SURVEYS 

1.  Scope  and  Importance  of  Current  Measurements. 

Under  the  head  of  current  measurements  are  included  all  ob- 
servations of  current  flow  obtained  by  ammeter  readings,  or  by  a 
potential  drop  on  a  conductor,  the  resistance  of  which  is  approxi- 
mately known.  They  include  measurements  of  current  flowing 
from  subsurface  structures  into  the  earth. 

Current  measurements  on  undrained  structures  made  both  before 
and  after  a  change  in  the  railway  system  or  the  application  of  other 
mitigative  measures  afford  considerable  information  as  to  the 
change  in  electrolysis  conditions.  Owing  to  the  great  variety  of 
conditions  under  which  it  is  at  times  necessary  to  measure  cur- 
rent, as  in  copper  feeders,  rails,  pipes,  cable  sheaths,  and  even 


ELECTROLYSIS  SURVEYS  109 

in  portions  of  the  soil,  the  methods  of  procedure  may  vary  con- 
siderably. 

2.  Measurement  of  Currents  in  Feeders  and  Rails. 

(a)  Purpose  of  Measuring  Feeder  and  Rail  Currents.     Measure- 
ments of  current  in  track  feeders  and  rails  are  usually  made  only 
when  it  is  desired  to  check  the  current  distribution  in  a  network 
of  tracks.     Current  measurements  on  the  track  will  show  the 
points  at  which  additional  track  feeders  are  required  in  order  to 
limit  potential  gradients  in  the  track  as  well  as  the  amount  of 
current  that  must  be  taken  off  at  each  point,  and  consequently 
the  sizes  of  feeders  required.   The  same  result  can  be  obtained  with 
sufficient  accuracy  for  most  practical  purposes  by  the  use  of  a 
"spot  map"  on  which  are  shown  the  average  distribution  of  cars 
and  their  corresponding  loads.     Further,  by  measuring  current  in 
different  rails  in  the  track,  local  bad  bonding  will  be  revealed 
since  unequal  distribution  of  current  always  indicates  relatively 
high  resistance  in  the  rails  carrying  the  lower  currents.     In  fact, 
some  engineers  regard  the  measurement  of  the  relative  current 
in  the  rails  at  a  number  of  points  as  the  most  reliable  way  of 
obtaining  in  a  short  time  a  good  idea  of  the  condition  of  track 
bonding. 

(b)  Procedure   in   Measuring   Current   in   Feeders   and   Rails. 
The  most  accurate  method  of  measuring  current  in  a  feeder  of 
rail  is  of  course,  afforded  by  inserting  an  ammeter  shunt  directly 
in  series  with  the  feeder  or  rail  under  test.     However,  in  practice 
it  often  happens  that  in  the  case  of  negative  feeders  ammeters  or 
shunts  are  not  provided  and  can  be  inserted  only  with  difficulty, 
and  in  the  case  of  rails  this  is  impracticable.     The  most  common 
method,  therefore,  of  measuring  current  in  such  structures  is  to 
measure  the  potential  drop  on  a  known  length  of  cable  or  rail 
and  to  calculate  the  current  from  this  potential  drop  and  the 
resistance    of   the    conductor.     Such    measurements   of   current 
can  be  made  on  copper  cables  with  high  accuracy  and  on  steel 
rails  the  results  can  usually  be  relied  upon  to  10  per  cent  or  better, 
which  is  sufficient  for  practically  all  purposes.     In  making  the 
current  calculations  it  is  customary  to  consider  the  resistivity  of 
the  copper  at  10.7  ohms  per  circular  mil-foot,  and  that  of  steel 
rails  to  be  0.0003  ohm  per  pound-foot,  this  latter  being  equivalent 
to  a   resistance    of   0.000009  ohm  for  one  foot  of  rail  weighing 
100  pounds  per  yard.     In  practice  it  may  be  expected,  however, 
that  the  resistance  per  pound-foot  may  vary  between  the  values 


110  ELECTROLYSIS  SURVEYS 

of  0.00027  and  0.00033,  or  about  ten  per  cent  each  way  from  the 
mean  values  here  given.  Table  5  in  the  appendix  will  be  found 
convenient  for  calculating  the  current  in  rails  of  various  weights. 

3.  Measurement  of  Currents  in  Pipes  and  Cable  Sheaths. 

(a)  Purpose  and  Importance  of  Pipe  Current  Measurements. 
The  measurement  of  current  in  pipes  and  lead  cable  sheaths  is 
important  for  a  number  of  reasons.     Heavy  currents  in  pipes  are 
often  objected  to  by  owners  of  pipe  networks,  particularly  gas 
and  oil  pipes  owing  to  the  fear  that  trouble  may  result  from 
ignition  of  gas  or  oil  due  to  arcing  when  two  portions  of  the 
pipe  network  are  separated,  and  also  due  to  arcing  between  adja- 
cent pipes  in  confined  air  spaces  such  as  cellars  where  there  may 
be  considerable  potential  differences  due  to  such  currents.     In 
some  cases  also,  excessive  heating  has  resulted  due  to  the  presence 
of  abnormally  large  currents  on  small  pipes,  and  the  presence  of 
such  heavy  currents  may  make  it  very  difficult  to  prevent  local 
interchange  of  current  between  neighboring  structures.     Heavy 
currents  on  lead  power  cables  are  also  objectionable  because  the 
heat  generated  in  the  lead  sheath  may  limit  considerably  the 
carrying  capacity  of  the  conductors  within  the  sheath.     In  view 
of  these  factors,  it  becomes  important  to  measure  currents  on 
pipes  and  cables  in  many  instances.     Relative  current  measure- 
ments on  pipe  and  cable  systems  made  before  and  after  the 
application  of  mitigative  measures  are  also  valuable  as  an  index 
of  the  effectiveness  of  the  mitigative  system  employed.     This  is 
true,  however,  only  when  there  has  been  no  installation  of  new 
drainage  connections  or  change  in  existing  drainage  connections 
on  the  affected  structures. 

(b)  Selection  of  Points  of  Measurement.     In  general  in  selecting 
points  for  making  current  measurements,  it  is  desirable  to  secure 
some  points  at  which  maximum  current  flow  may  be  anticipated, 
and  also 'a  considerable  number  of  points  that  may  be  regarded 
as  representative  of  conditions  generally.     As  a  rule,  the  maximum 
current  in  an  undrained  pipe  network  may  be  expected  in  pipes 
extending  approximately  parallel  to  the  tracks  and  near  the 
neutral   or   slightly   positive   areas.     Also   numerous   cases  will 
usually  be  found  in  any  network  in  which  one  or  at  most,  a  few 
mains  serve  as  connecting  links  between  local  networks,  and  such 
mains  usually  will  be  found  to  carry  much  larger  currents  than 
mains  forming  a  portion  of  the  network.     On  drained  pipe  systems, 
the  maximum  currents  will  as  a  rule  be  found  in  the  pipes  extend- 


ELECTROLYSIS  SURVEYS  111 

ing  in  all  directions  from  the  points  at  which  drainage  cables  are 
connected.  It  is  impossible  to  lay  down  rules  more  detailed  than 
the  above  for  the  selection  of  points  at  which  measurements 
should  be  made.  Experienced  judgment  should  be  followed  in 
all  cases. 

(c)  Methods  of  Measuring  Current  Flow  in  Pipes.  Four  general 
classes  of  methods  of  measuring  current  flow  in  pipes  and  other 
metallic  structures  have  been  used.  The  one  that  is  perhaps  the 
most  frequently  used  is  the  ordinary  drop-in-potential  method  in 
which  the  voltage  drop  on  a  measured  length  of  pipe,  not  in- 
cluding a  joint,  is  taken  and  the  current  calculated  from  this 
voltage  drop  and  the  estimated  resistance  of  the  portion  of  the 
pipe  across  which  the  potential  drop  is  measured.  Complete 
tables  for  the  resistance  per  unit  length  of  the  various  sizes  and 
kinds  of  pipe  in  common  use  are  given  in  the  appendix.  Careful 
tests  made  on  a  great  variety  of  specimens  of  pipe  of  different 
kinds,  indicate  that  measurements  of  this  kind  can  be  depended 
upon  to  give  results  accurate  to  within  about  10  per  cent,  which 
is  ample  in  most  cases  encountered  in  practice. 

A  second  method,  used  in  special  cases  where  greater  accuracy 
than  is  possible  by  the  drop-in-potential  method  is  necessary,  is 
the  method  for  calibrating  the  pipe  either  by  sending  a  known 
current  through  it  superposed  on  the  railway  current  already 
flowing  in  the  pipe,  or  by  shunting  through  an  ammeter,  certain 
portions  of  the  current  actually  flowing  in  the  pipe.  These 
methods  have  taken  various  forms,  one  of  the  most  important  of 
which  is  described  later. 

A  third  method  consists  in  the  use  of  what  is  known  as  a  direct 
current  ratio  relay  in  a  manner  somewhat  analogous  to  the  use  of 
a  current  transformer  on  alternating  current  circuits.  This  is 
useful  only  where  currents  of  fifty  amperes  or  more  flow  on  the 
pipe. 

A  fourth  method  consists  in  surrounding  the  pipe  with  an  iron 
ring  containing  an  airgap  and  providing  means  for  measuring  the 
magnetic  flux  set  up  across  the  airgap  by  the  current  in  the  pipe. 
Several  different  methods  are  available  for  making  these  measure- 
ments. The  last  two  methods  may  also  be  used  for  calibrating  the 
pipes,  thus  eliminating  in  some  measure  the  uncertainty  arising 
from  the  calculation  of  the  pipe  resistance.  It  is  questionable, 
however,  whether  in  most  cases  the  greater  accuracy  thus  achieved 
is  sufficient  to  warrant  the  use  of  the  more  complicated  methods. 


112 


ELECTROLYSIS  SURVEYS 


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ELECTROLYSIS  SURVEYS  113 

There  are  given  below  somewhat  detailed  descriptions  of  the  first 
two  of  these  methods. 

Drop-in-Potential  Method.  This  method  consists  in  connecting 
potential  terminals  to  a  section  of  pipe  a  few  feet  apart  and  meas- 
uring the  millivolt  drop,  and  in  calculating  the  current  from  this 
millivolt  drop  and  the  resistance  of  the  section  under  test.  It  is 
very  widely  used,  and  its  great  simplicity  adapts  it  to  work  of  this 
kind.  This  method  has  the  great  advantage  that  it  can  not  only 
be  used  with  an  indicating  instrument  but  also  with  a  recording 
instrument  unless  the  currents  are  very  small,  and  thus  not  only 
a  permanent  graphic  record  be  obtained,  but  also  the  average  value 
for  a  given  period  can  be  determined.  The  tables  appended  to 
this  report  are  based  on  careful  measurements  made  by  the  Bureau 
of  Standards  on  several  hundred  specimens  of  iron  and  lead  pipes 
from  various  sources,  and  they  are  accurate  enough  for  all  prac- 
tical purposes. 

In  using  this  method  it  is  necessary  to  make  an  excavation  at 
the  point  where  the  measurement  is  to  be  taken  and  attach  two 
leads  to  the  pipe,  preferably  as  far  apart  as  practicable  without 
including  a  joint.  This  connection  may  be  made  in  numerous 
ways,  but  perhaps  the  best  way  is  to  insert  at  each  point  a  corpora- 
tion cock  in  which  a  rubber  covered  wire  has  been  soldered.  If 
the  connections  are  to  be  permanent,  the  leads  should  be  brought 
underground  to  a  point  inside  the  curb  and  there  terminated  in  an 
ordinary  service  box  or  other  suitable  receptacle  so  that  they  will 
be  protected  from  traffic  but  readily  accessible  for  repeating  the 
measurement  at  any  time.  One  method  of  making  such  connec- 
tions and  protecting  the  leads  is  shown  in  Fig.  21,  and  another 
which  has  been  very  successfully  used  in  paved  streets  is  shown 
in  Fig.  22.  It  is  also  important  that  the  junction  between  wire 
and  corporation  cock  be  protected  by  painting  with  a  heavy  as- 
phalt or  similar  paint.  If  the  current  on  the  pipe  is  large  enough 
to  be  of  practical  significance  it  can  be  read  with  an  ordinary 
sensitive  millivoltmeter  either  indicating  or'  recording.  In  special 
cases  where  the  current  is  extremely  small,  only  a  high  sensitivity 
indicating  millivoltmeter  or  even  a  portable  galvanometer  can  be 
used. 

Calibration  of  Pipes.  One  of  the  methods  most  commonly 
used  for  the  calibration  of  pipes  involves  superposing  a  current  on 
that  already  in  the  pipe  and  measuring  the  change  in  millivolt 
drop  due  to  this  superposed  current.  This  method,  originally 
used  by  Professor  B.  F.  Thomas  was  first  described  by  Dr.  Carl 


114 


ELECTROLYSIS  SURVEYS 


ELECTROLYSIS  SURVEYS  115 

Hering  in  the  Transactions  of  the  American  Institute  of  Electrical 
Engineers  for  June,  1912.  Theoretically,  this  method  should 
give  very  high  accuracy,  but  it  should  be  borne  in  mind  that  the 
resistance  of  the  pipe  thus  determined  is  correct  only  for  the 
conditions  under  which  the  measurement  was  made.  Iron  pipes, 
especially  wrought  iron  and  steel  pipes,  have  a  high  temperature 
coefficient  of  resistance  and  variations  in  this  resistance  due  to 
temperature  changes  between  winter  and  summer  may  introduce 
variations  of  .five  per  cent  or  more  in  this  resistance.  For  this 
reason,  it  is  very  doubtful  whether  the  complication  involved  in 
the  use  of  this  method  is  justified,  but  it  has  been  used  by  some 
engineers.  Further,  owing  to  the  presence  of  rapidly  fluctuating 
railway  currents  on  the  pipes,  the  application  of  this  method  is 
often  difficult. 

Use  of  a  Direct-Current  Ratio  Relay.  An  instrument  known  as 
the  direct-current  ratio  relay  for  measuring  current  in  conductors 
which  cannot  be  opened  for  the  insertion  of  ammeters  or  shunts 
has  recently  been  devised.  The  ratio  relay  permits  the  measure- 
ment of  variable  unidirectional  currents  of  relatively  large  magni- 
tude only,  on  an  ordinary  direct  current  ammeter.  This  instru- 
ment gives  very  good  results  when  very  large  currents  are  being 
measured,  but  in  its  present  form  it  is  not  suitable  for  measuring 
currents  of  a  few  amperes,  such  as  are  most  frequently  encountered 
in  electrolysis  testing. 

4.  Comparing  Currents  Under  Different  Conditions. 

In  case  the  object  in  view  is  the  determination  of  relative  cur- 
rent in  pipes  under  different  systems  of  mitigation,  this  can  be 
done  simply  by  measuring  potential  drops  between  services  or 
between  adjacent  fire  hydrants.  In  general,  the  resistance  may 
be  regarded  as  sufficiently  constant  so  that  the  currents  under  the 
two  conditions  of  test  will  be  proportional  to  the  voltages  at 
corresponding  test  stations. 

5.  Measurement  of  Current  Flowing  from  Underground  Struc- 
tures to  Earth. 

It  is  extremely  desirable  to  measure  the  amount  of  current 
flowing  from  a  particular  portion  of  a  pipe  or  cable  network 
directly  into  the  earth.  In  fact,  if  such  measurements  could  be 
made  conveniently  and  with  sufficient  accuracy  they  would  be  by 
far  the  most  important  and  valuable  measurements  that  could  be 
made  in  an  electrolysis  survey,  since  this  measurement  would 
afford  the  most  accurate  measure  of  the  rate  at  which  damage  is 


116  ELECTROLYSIS  SURVEYS 

progressing.  Unfortunately,  there  has  not  been  available  up  to 
the  present  time,  any  very  satisfactory  method  of  measuring  such 
current  flow  except  in  very  special  cases.  Four  different  methods 
have  been  proposed  under  special  conditions  for  making  this 
measurement.  These  are:  (a)  differential  current  measurements; 
(b)  the  use  of  a  Haber  earth  current  collector;  (c)  the  measurement 
of  polarization  potentials;  and  (d)  the  combined  measurement  of 
potential  drop  and  earth  resistivity.  The  first  of  these  is  dis- 
cussed below.  The  second  and  third  have  been  found  impractical 
and  the  last  is  still  under  development. 

(a)  Differential  Current  Measurement.  This  method  of  measur- 
ing current  flow  from  a  pipe  to  earth  can  be  used  to  advantage 
where  it  is  desired  to  measure  a  current  discharge  that  is  com- 
parable in  magnitude  with  the  total  current  on  the  pipe.  If  the 
measurement  is  made  at  two  points  on  the  pipe  by  the  potential 
drop  method,  uncertainties-  in  the  measured  values  may  be  too 
great  to  permit  an  accurate  determination  of  discharge,  but  if  the 
pipes  are  carefully  calibrated  at  the  points  at  which  the  potential 
drops  are  measured,  fairly  accurate  results  can  be  obtained, 
provided  the  difference  in  current  is  as  mtlch  as  ten  or  fifteen  per 
cent  of  the  total  current  flowing  in  the  section  of  the  pipe  under 
test.  In  making  current  discharge  measurements  by  this  method, 
it  is  necessary  to  make  sure  that  there  are  no  service  pipes  or 
drainage  feeders  connected  with  the  portion  of  the  pipe  between 
test  points  through  which  current  may  flow. 

C.     MISCELLANEOUS  TESTS 
1.  Track  Testing. 

Electrical  tests  are  made  on  railway  tracks  chiefly  for  three 
purposes — first,  to  locate  the  cause  of  bad  electrolysis  conditions 
that  may  have  been  encountered — second,  to  serve  as  a  guide  for 
the  systematic  maintenance  of  the  railway  track  network,  and 
third — to  be  used  as  a  guide  in  designing  an  electrolysis  mitigation 
system.  Three  methods  of  determining  the  condition  of  the  track 
system  have  been  extensively  used,  as  follows : 

(a)  Inspection.  This  method  of  testing  bonds  by  a  simple 
inspection  is  one  which  has  been  used  much  more  extensively  in 
the  past  than  at  the  present  time,  but  it  is  unfortunately  still 
very  frequently  used  in  open  track  work.  It  consists  chiefly  in 
going  along  the  track  and  making  superficial  inspection  of  the 
bonds  and  if  they  appear  mechanically  good,  the  assumption  is 
made  that  the  bond  is  in  a  satisfactory  condition.  It  cannot  be 


ELECTROLYSIS  SURVEYS  117 

too  strongly  emphasized  that  any  examination  of  bonds  by  this 
simple  method  of  inspection  should  be  regarded  as  a  poor  make- 
shift, and  some  more  reliable  method  should  always  be  used. 

(b)  Use  of  Portable   Bond   Tester.     There  are  in  use  at  the 
present  time  a  number  of  portable  bond  testers  operating  on  the 
principle  of  a  slide  wire  bridge,  a  portable  milli voltmeter  being 
used  to  determine  when  the  bridge  is  balanced.     In  the  use  of 
this  instrument  the  voltage  drop  across  the  joint  is  compared 
directly  by  the  bridge  method  with  the  voltage  drop  on  a  definite 
length  of  rail  directly  adjacent  to  the  joint  under  test,  so  that  the 
resistance  of  the  joint  is  measured  in  terms  of  an  equivalent  length 
of  rail.     This  method  has  the  advantage  of  simplicity  as  it  can  be 
operated  by  one  man,  and  while  somewhat  slow  and  tedious.it 
often  affords  a  very  satisfactory  method  of  testing  bonds. 

(c)  Autographic  Method  of  Bond  Testing. — A  method  that  has 
been  used  extensively  in  recent  years  for  testing  the  bonds  in 
railway  tracks  is  what  is  known  as  the  autographic  method.     This 
method  is  like  that  of  the  portable  bond  tester  in  that  it  is  based 
on  a  comparison  of  the  potential  drop  across  a  certain  length  of 
rail,   including  the  joint,   with  that  across  an  equal  length  of 
adjacent  solid  rail.     The  two  readings  are  taken  and  automatically 
recorded  within  a  fraction  of  a  second,  and  during  this  short  time, 
the  current  in  the  rail  may  be  regarded  as  practically  constant. 
The  method,  however,  permits  of  a  correction  in  case  the  current 
should  vary  appreciably  between  two  readings.     The  autographic 
method  has  several  advantages,  chief  of  which  are  as  follows: 

(1)  A  special  test  current  is  employed  so  that  one  does  not  have 
to  depend  on  the  railway  load  which  is  uncertain  and  at  times 
discontinuous. 

(2)  It  eliminates  the  personal  element  to  a  large  extent,  all 
readings  being  autographic. 

(3)  It  gives  a  permanent  record  which  can  be  kept  on  file  for 
future  reference. 

(4)  A  large  amount  of  track  can  be  covered  in  a  short  time  so 
that  the  test  of  an  entire  railway  system  can  quickly  be  made  at 
any  particular  period. 

The  apparatus  for  this  method  of  testing  is  quite  expensive  as 
a  special  car  is  required  and  sometimes  another  car  is  used  to  haul 
the  test  car.  Owing  to  the  much  greater  rate  at  which  bonds  can 
be  tested  by  this  method,  however,  the  total  cost  on  a  large  job 
will  not  necessarily  be  greater  than  with  manual  testing. 

(d)  Testing   of    Cross-bonds    and   Special-Work   Jumpers.     In 


118 


ELECTROLYSIS  SURVEYS 


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ELECTROLYSIS  SURVEYS  119 

addition  to  testing  the  joints  discussed  above,  it  is  important  also 
to  test  the  condition  of  cross-bonds  between  rails  and  of  jumpers 
spanning  special  work.  This  can  perhaps  best  be  done  by  means 
of  a  low  reading  voltmeter  having  two  ranges  from  .01  to  one  volt, 
the  test  being  made  by  going  along  the  track  and  measuring  the 
potential  difference  between  the  various  rails  at  frequent  intervals, 
and  also  across  various  sections  of  special  work. 

2.  Measurement  of  Leakage  Resistance  between  Tracks  and 
Underground  Structures. 

(a)  Importance  of  Tests  of  Roadbed  Resistance. — The  determina- 
tion of  the  average  resistance  of  the  leakage  path  between  railway 
tracks  and  surrounding  earth  is  often  very  desirable,  particularly 
where  it  is  necessary  to  determine  what  overall  potential  drops 
may  safely  be  permitted  in  the  track  return.     It  will  be  evident 
that  if  the  resistance  of  the  leakage  paths  is  very  high,  it  will  be 
safe  to  allow  higher  potential  drops  in  the  track  than  if  the  leakage 
resistance  be  low,  although  the  voltage  drop  which  may  be  con- 
sidered safe  is  not  directly  proportional  to  the  average  resistance 
of  the  leakage  path. 

(b)  Differential  Method  of  Measuring  Roadbed  Resistance.     Fig. 
23  illustrates  the  method  employed  for  making  measurements  on 
roadbeds  where  it  is  found  impracticable  to  isolate  a  limited  section 
of  the  track.     After  the  car  traffic  has  been  withdrawn  for  the 
night,  a  portable  storage  battery  is  connected,  as  shown,  between 
the  four  rails  of  the  track  and  a  fire  hydrant  on  a  relatively  large 
main.     An  ammeter  and  a  regulating  resistance  are  included  in 
the  circuit.     A  ten  volt  storage  battery  or  a  low  voltage  generator 
is  employed  for  this  purpose  and  a  constant  current  of  from  twenty 
to  forty  amperes  is  maintained  during  the  period  of  the  test.     The 
current  entering  the  rails  will  flow  away  from  the  test  station  in 
both  directions,  as  shown  by  the  arrows.     Leakage  will  take  place 
to  the  earth  and  all  of  the  current  will  be  picked  up  by  the  water- 
piping  system  and  returned  to  the  negative  pole  of  the  battery. 
If  now  a  milli voltmeter  be  employed  to  measure  the  potential 
drop  on  a  short  section  of  the  track  at  Station  A,  and  again  at 
several  thousand  feet  distant  at  Station  B,  the  loss  of  current 
from  the  rails  between  the  two  stations  can  at  once  be  determined, 
provided  the  rails  are  of  the  same  weight  and  resistivity  at  the  two 
stations,  and  provided  further,  that  the  battery  current  has  re- 
mained constant.     Now,  if  the  potential  difference  between  the 
section  of  track  under  test  and  the  earth  at  some  distance  from  it 


120 


ELECTROLYSIS  SURVEYS 


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ELECTROLYSIS  SURVEYS  121 

be  measured,  the  resistance  to  earth  of  this  section  of  track  can 
easily  be  computed. 

While  the  principle  involved  in  such  a  measurement  is  extremely 
simple,  the  practical  difficulties  encountered  make  accurate  and 
reliable  results  very  difficult  of  attainment,  and  it  is  only  by  many 
and  repeated  measurements  that  reliable  data  can  be  secured. 
The  difference  between  the  currents  at  Stations  A  and  B  is  the 
quantity  which  must  be  determined,  and  as  this  is  usually  a  small 
fraction  of  the  total  current,  even  over  a  distance  of  one-half 
mile,  a  slight  error  in  the  measurements  would  be  exaggerated  in 
the  result.  Errors  might  result  from  inaccurate  readings  or  from 
different  rail  weights  or  resistivities.  It  is  necessary,  therefore, 
to  make  not  only  one  measurement  on  each  of  the  four  rails  at 
both  stations,  but  measurements  should  be  made  at  several  slightly 
different  locations  at  each  station. 

Tn  determining  the  average  potential  difference  between  the 
track  and  the  earth,  voltage  measurements  should  be  made  to  as 
many  different  underground  structures  as  can  be  found  in  the 
vicinity.  Measurements  made  to  the  fire  hydrants  along  the 
track  are  likely  to  give  erroneous  results,  due  to  the  gradient  on 
the  water  main  caused  by  the  return  current.  The  most  reliable 
and  consistent  results  are  obtained  by  driving  a  ground  rod  into 
the  earth  at  a  distance  of  not  less  than  200  feet  from  the  track 
and  measuring  the  potential  difference  between  it  and  the  track 
with  a  high  resistance  voltmeter. 

(c)  Isolation  Method  of  Measuring  Roadbed  Resistance.  When 
it  is  desired  to  make  measurements  in  localities  where  no  piping 
systems  exist,  the  method  just  described  cannot  be  employed. 
These  roadbeds  are  usually  of  open  construction  and  it  is  there- 
fore a  comparatively  simple  matter  to  remove  the  joint  plates 
and  bonds  from  four  joints,  thus  isolating  a  section  of  track  on 
which  accurate  and  reliable  measurements  can  be  made.  Fig. 
24  shows  the  arrangement  of  the  apparatus  for  this  test.  A 
section  of  track  from  100  to  500  feet  in  length  is  isolated  from  the 
remainder  of  the  track  network  by  removing  the  bonds  and  joint 
plates  as  shown.  All  cross  bonds  between  this  test  section  and 
the  adjacent  track  must  also  be  cut.  A  battery  of  three  or  four 
dry  cells  is  connected  between  the  test  section  and  the  remainder 
of  the  track  network,  which,  being  of  great  extent,  is  considered 
as  a  remote  ground  of  negligible  resistance.  A  low-reading  am- 
meter and  a  voltmeter  give  the  current  flowing  and  the  potential 
difference  between  the  section  of  the  track  under  test  and  the 


122  ELECTROLYSIS  SURVEYS 

remote  ground,  and  from  these  data  the  resistance  to  earth  is 
easily  and  accurately  calculated. 

By  taking  several  hundred  feet  of  track,  the  effect  of  the  short 
leakage  paths  at  the  ends  of  the  section  is  practically  eliminated. 

The  resistance  so  found  is  for  a  single-track  roadbed  but  in  the 
open  type  of  construction  the  resistance  to  earth  is  concentrated 
largely  in  the  ties  and  therefore  the  resistance  of  double  track  can 
be  taken  as  one-half  that  of  single  track.  This  is  not  true  when 
the  rails  are  imbedded  in  earth  or  concrete.  In  this  case  the  re- 
sistance of  a  double  track  may  be  taken  as  about  seventy  per 
cent  of  that  of  a  single  track  if  only  approximate  results  are  re- 
quired. This  method  of  measuring  roadbed  resistances  necessi- 
tates working  at  night,  as  does  the  differential  method,  since  it 
usually  requires  several  hours  to  remove  and  replace  the  bonds 
and  joint  plates  on  four  joints. 

3.  Location  and  Testing  of  High-Resistance  Joints  in  Pipes. 

In  making  electrolysis  surveys,  it  is  often  necessary  to  determine 
whether  or  not  there  are  any  considerable  number  of  high  resist- 
ance joints  in  a  given  portion  of  a  pipe  network.  This  has  been 
a  particularly  important  test  in  making  investigations  of  joint 
electrolysis  in  pipe  systems,  and  may  often  be  useful  in  determin- 
ing upon  the  method  of  protection  to  be  used  in  particular  cases. 
High-resistance  joints  may  be  most  conveniently  located  by  means 
of  potential  drop  measurements  along  the  pipes.  The  method 
usually  followed  is  to  drive  bars  down  until  they  come  in  contact 
.with  the  pipe  and  measure  the  potential  drop  on  the  pipe  at  such 
points,  the  spacing  of  the  points  being  usually  about  100  feet. 
A  series  of  such  measurements  is  made  throughout  the  entire 
length  of  the  pipe  and  the  relative  magnitudes  of  the  voltage  drops 
on  adjacent  sections  would  indicate  which,  if  any,  is  affected  by 
high  resistance  in  the  pipe  line.  When  it  has  been  determined 
that  any  particular  hundred-foot  length  includes  one  or  more 
high  resistance  joints,  this  section  can  be  further  subdivided  by 
exactly  the  same  procedure  until  a  relatively  high  drop  is  obtained 
between  two  points  less  than  a  pipe  length  apart,  which  must  in- 
clude a  high  resistance  joint.  By  comparing  the  drop  across  the 
the  high  resistance  joint  with  the  drop  in  a  measured  distance  on 
continuous  pipe,  the  resistance  of  the  joint  in  terms  of  equivalent 
feet  of  pipe  can  be  obtained. 


ELECTROLYSIS  SURVEYS  123 

4.  Tracing  the  Source  of  Stray  Currents. 

Conditions  are  often  encountered  in  which  stray  currents  on 
pipe  networks  may  come  from  any  one  of  two  or  more  railway  lines, 
and  it  is  important  to  determine  from  which  line  the  current  is 
derived.  This  can  be  determined  in  either  of  two  ways.  One 
method  is  to  connect  a  measuring  instrument  of  the  recording  type 
to  the  pipe  under  test,  which  may  be  connected  either  to  indicate 
the  current  flow  along  the  pipe  or  the  potential  difference  between 
the  pipe  and  the  earth.  With  the  instrument  thus  connected,  a 
record  is  obtained,  while  all  railway  systems  are  operating  under 
normal  conditions.  Then  one  of  the  railway  systems  is  shut 
down  for  as  long  a  period  as  practicable.  If  the  shutting  down  of 
the  plant  makes  a  marked  difference  in  the  record,  it  is  an  indica- 
tion that  a  large  part  of  the  stray  current  at  least  comes  from  that 
particular  point.  By  shutting  down  the  different  systems  in 
rotation,  a  fairly  definite  knowledge  of  the  source  of  the  stray 
current  may  be  obtained.  Sometimes  it  will  be  found  that  the 
shutting  down  of  one  plant  increases  the  current  flow  in  one 
direction,  while  shutting  down  another  plant  may  give  rise  to  a 
large  current  flow  in  the  opposite  direction,  both  currents  being 
larger  than  when  both  plants  are  running.  This  will  indicate  that 
the  stray  current  from  the  two  systems  tend  to  neutralize  each 
other,  thus  giving  rise  to  better  conditions  in  certain  localities 
than  those  which  prevail  when  either  system  is  operating  alone. 

The  other  method  of  tracing  the  source  of  stray  current  in  any 
particular  case  consists  in  the  use  of  two  or  more  recorders,  one 
of  which  makes  a  graphic  record  of  the  current  or  voltage,  the 
source  of  which  is  to  be  determined,  while  the  others  are  used  to 
make  simultaneous  records  of  the  loads  on  the  various  power 
supply  stations  which  may  possibly  affect  the  area  in  question, 
or  more  particularly  the  loads  on  certain  feeders  from  those  sta- 
tions. In  most  cases  there  will  be  sufficient  similarity  between  the 
chart  of  the  stray  current  and  some  one  of  the  feeder  or  station 
load  charts  to  establish  quite  definitely  the  source  of  the  stray 
current. 

5.  Location  of  Unknown  Metallic  Structures  or  Connections. 

It  is  often  desirable  to  locate  metallic  connections  between  pipes 
and  various  other  structures,  such  as  railway  track  returns  which 
may  often  exist  without  the  knowledge  of  either  the  pipe  or  rail- 
way company.  Two  methods  are  available  for  doing  this:  One 
consists  in  connecting  an  external  electrical  circuit  between 


124  ELECTROLYSIS  SURVEYS 

convenient  points  on  the  pipe  system  and  railway  system,  and 
sending  between  them  either  an  alternating  current  of  audible 
frequency  or  a  direct  current  interrupted,  at  audible  frequency. 
An  exploring  coil  is  then  carried  along  the  pipe  system  in  such 
position  that  the  alternating  or  pulsating  magnetic  field  produced 
by  the  current  superposed  on  the  pipe  current  will  induce  an  elec- 
tromotive force  in  the  coil.  This  can  be  made  audible  by  the  use 
of  a  telephone  receiver.  By  this  instrument,  the  path  of  the 
current  can  be  traced  and  in  most  cases  the  location  of  concealed 
connections  to  the  pipe  can  be  determined.  The  method  works 
very  satisfactorily  on  relatively  simple  pipe  networks,  but  in  very 
complicated  systems  where  there  are  a  great  many  pipes  laid  in 
the  street  it  becomes  relatively  difficult  to  trace  out  any  particular 
structure. 

A  method  that  has  been  more  recently  developed  and  which  is 
considerably  more  simple  than  the  above,  consists  in  doing  away 
with  the  additional  current  superposed  on  the  pipe  network,  and 
using  the  exploring  coil  and  telephone  to  listen  to  the  commutation 
note  in  the  railway  current  carried  by  the  pipe.  This  method  is 
much  to  be  preferred  where  the  pipe  currents  are  large  enough  to 
give  sufficient  sensitivity.  In  some  cases,  however,  where  the 
currents  on  the  pipe  are  very  small,  the  first  method  may  have  to 
be  resorted  to. 

in.  INTERPRETATION   OF  RESULTS   OF  ELECTROLYSIS 

SURVEYS 

No  definite  rules  of  procedure  can  be  laid  down  for  the  interpre- 
tation of  the  results  of  electrolysis  surveys  that  can  be  used 
except  by  engineers  thoroughly  familiar  with  all  the  factors  in- 
volved. The  significance  of  any  particular  set  of  readings  is  so 
dependent  upon  other  conditions  that  all  factors  must  be  taken 
into  account  or  else  the  conclusions  are  likely  to  be  in  error. 
However,  it  is  desirable  to  point  out  certain  principles  that  must 
be  kept  in  mind  even  by  the  experienced  engineer  in  order  to 
arrive  at  correct  conclusions. 

A.  INTERPRETATION  OF  POTENTIAL  MEASUREMENTS 
1.  Maximum  Voltages  and  Track  Gradients. 

These  measurements,  when  considered  in  the  light  of  a  full 
knowledge  of  all  conditions,  give  valuable  data  on  the  condition 
of  the  railway  track  system  and  the  concentration  of  return  current 
on  certain  sections  of  track.  They  also  are  valuable  when  con- 
sidered in  the  light  of  the  load  on  the  different  lines,  as  they  offer 


ELECTROLYSIS  SURVEYS  125 

a  fairly  accurate  indication  of  the  track  losses  and  the  necessity 
for  the  use  of  additional  track  feeders.  When  such  potential 
measurements  are  taken  over  relatively  short  lengths  of  track,  such 
as  1,000  or  2,000  feet,  the  comparison  of  such  measurements  on 
adjacent  sections  of  track  will  often  reveal  bad  places  in  the  track 
that  are  in  need  of  rebonding.- 

2.  Potential  Difference  Measurements. 

Potential  difference  readings  between  pipes  and  railway  tracks 
and  between  various  underground  structures  are  not  a  quantita- 
tive measure  of  the  danger  to  the  affected  structures.  These 
readings  are  valuable  in  pointing  out  the  general  areas  in  which 
trouble  may  be  expected  to  occur  and  in  which  more  careful 
search  may  be  made  if  desired.  They  are,  however,  of  qualitative 
significance  only.  The  current  leaving  a  structure  for  the  earth 
in  any  locality,  which  is  the  real  cause  of  the  electrolysis  damage, 
is  a  function  not  only  of  the  potential  differences  but  of  the  re- 
sistance of  the  earth  paths.  This  has  been  shown  to  vary  through- 
out extremely  wide  limits,  so  that  the  measurement  of  potential 
difference  gives  no  definite  quantitative  measurement  of  the 
extent  of  the  hazard  to  the  pipes.  Such  measurements  are  very 
valuable  and  have  an  accurate  quantitative  significance,  however, 
when  used  to  determine  the  relative  electrolysis  conditions  under 
different  systems  of  mitigation.  If,  for  example,  under  a  given 
set  of  conditions  a  considerable  number  of  potential  difference 
measurements  are  made  between  the  various  underground  struc- 
tures and  then  a  change  is  made  in  the  mitigative  system,  and  the 
same  measurements  repeated,  the  two  sets  of  readings  may  be 
used  to  represent  the  comparative  hazard  in  the  two  cases.  This 
is  true  only  if  the  mitigative  measures  under  test  are  applied 
exclusively  to  the  railway  return  system. 

High  potential  differences  between  gas  and  oil  pipes  and  other 
metallic  structures  with  which  they  may  come  in  contact  are 
objectionable  especially  in  confined  spaces,  such  as  basements 
in  which  explosive  mixtures  may  be  encountered.  This  is  because 
a  transient  contact  between  the  two  structures  may  cause  an  arc 
which  may  result  in  fire  or  explosion. 

B.  INTERPRETATION  OF  CURRENT  MEASUREMENTS  ON 

UNDERGROUND  STRUCTURES 
1.  Relation  of  Stray  Current  to  Corrosion. 

The  magnitude  of  the  current  on  an  underground  structure  does 
not  alone  afford  a  measure  of  the  total  injury,  to  the  structure. 


126  ELECTROLYSIS  SURVEYS 

If  all  the  current  that  flows  on  the  pipe  is  discharged  directly 
into  the  earth,  then  the  total  corrosion  will  be  approximately 
proportional  to  the  current  flow.  Even  here,  however,  the  rate 
of  damage  to  the  pipes  is  not  only  a  function  of  the  total  weight  of 
metal  corroded  away,  but  of  the  distribution  of  such  corrosion  as 
a  result  of  pitting  or  of  localized  discharge  from  one  system  to 
another  where  they  approach  close  to  each  other.  Further,  if 
there  are  metallic  connections  either  known  or  unknown  between 
portions  of  the  pipe  networks  and  the  railway  tracks,  which  carry 
off  a  large  part  of  the  current  on  the  pipe  through  metallic  paths, 
the  total  amount  of  corrosion  cannot  be  determined  by  measure- 
ment of  the  current  flow.  For  this  reason  current  measurements 
on  pipes  should  likewise  be  regarded  as  having  only  a  qualitative 
significance  in  so  far  as  any  absolute  hazard  to  the  pipes  is  con- 
cerned. If,  however,  the  pipes  have  no  drainage  connections 
and  changes  are  made  in  the  railway  track  network,  the  corre- 
sponding changes  in  the  currents  on  the  pipes  may,  if  a  sufficient 
number  of  readings  have  been  taken,  indicate  the  relative  im- 
provement in  the  electrolysis  conditions. 

2.  Relation  of  Current  to  Fires  and  Explosions. 

In  interpreting  the  significance  of  current  measurements  on 
gas  or  oil  pipes,  due  account  should  be  taken  of  the  possibility 
of  fires  and  explosions  due  to  arcs  formed  either  when  pipes  are 
disconnected,  or  when  pipes  make  transient  contact  in  confined 
places  such  as  cellars.  No  definite  information  is  at  present 
available  as  to  what  limiting  currents  on  such  pipes  may  be 
considered  safe,  but  it  is  generally  recognized  that  the  presence 
of  currents  on  gas  and  oil  lines  is  more  objectionable  than  in  the 
case  of  other  pipes. 

C.  INTERPRETATION  OF  MEASUREMENTS  OF  CURRENT 
FLOWING  FROM  STRUCTURES  TO  EARTH 

The  only  accurate  criterion  of  electrolysis  damage  is  the  in- 
tensity of  current  flow  to  earth  at  any  point  on  the  pipe  or  cable. 
If  an  accurate  measure  of  this  current  flow  from  the  pipe  at  any 
point  could  be  made,  it  would  come  nearer  giving  a  true  indication 
of  electrolysis  conditions  than  any  other  measurement.  At  the 
present  time  there  is  no  practical  means  available  for  making  such 
measurements.  The  development  of  a  simple,  inexpensive  and 
accurate  means  for  measuring  such  currents  locally,  constitutes 
one  of  the  chief  needs  in  the  field  of  electrolysis  testing  at  the 
present  time. 


ELECTROLYSIS  SURVEYS  127 

D.  USE  OF  REDUCTION  FACTORS 

In  many  cases  it  is  not  practicable  to  take  readings  of  current 
and  potential  at  any  point  over  a  sufficiently  long  time  to  get  all 
day  average  values  of  the  readings  at  that  point.  Such  readings 
should  always  be  taken  for  as  long  a  time  as  circumstances  permit, 
but  in  making  electrolysis  surveys,  it  is  usually  necessary  to 
take  a  large  number  of  readings  scattered  over  a  wide  area  so 
that  some  of  the  readings  can  be  continued  only  for  a  compara- 
tively short  time.  Such  short-time  readings  cannot,  in  general 
be  used  directly  as  a  basis  for  determining  electrolysis  conditions 
and  in  order  to  interpret  properly  the  results  of  the  survey,  the 
readings  must  be  reduced  to  some  common  basis,  as  for  example, 
either  the  twenty-four-hour  average,  the  operating-day  average, 
or  the  average  for  the  hour  of  the  peak  load.  Each  of  these  bases 
has  certain  advantages  and  disadvantages  depending  partly  on 
the  individual  conditions,  and  the  method  of  procedure  will  often 
differ,  depending  on  the  method  to  be  followed  in  interpreting 
the  results.  All  are  affected  by  such  factors  as  rush  or  light  days, 
unusual  weather  conditions,  electric  heaters  in  cold  weather, 
morning  and  evening  peak  loads,  and  other  causes,  and  these 
factors  must  be  considered. 

The  great  unreliability  of  short-time  readings  for  determining 
electrolysis  conditions  is  especially  noticeable  when  comparing 
the  load  curve  of  a  line  having  a  5,  10,  or  15  minute  schedule 
with  that  of  hourly  interurban  service,  or  when  comparing  that 
of  a  station  having  a  45  per  cent  load  factor  with  one  having  a 
load  factor  of  10  per  cent.  Because  of  this  great  variation  and 
uncertainity  in  short  time  measurements  and  for  the  purposes  of 
interpretation  and  comparison,  it  is  desirable  that  long  time 
readings  be  obtained,  but  if  this  is  impossible,  all  short-time  read- 
ings should  be  reduced  to  values  for  some  representative  period, 
preferably  the  twenty-four  hour  average. 

Experience  shows  that  in  the  majority  of  cases,  short-time 
readings  of  from  15  minutes  to  an  hour,  taken  on  a  city  network 
between  the  hours  of  10  A.  M.  and  about  4  P.  M.,  approach  rather 
closely  the  twenty-four-hour  average  values,  and  it  is  found  per- 
missible to  neglect  the  use  of  reduction  factors  in  connection 
with  readings  taken  during  this  period  of  the  day.  When,  how- 
ever, readings  are  taken  at  any  time  during  the  morning  or  evening 
peak,  or  after  nine  or  ten  o'clock  at  night,  it  is  necessary  to  use  a 
proper  reduction  factor  if  anything  like  reliable  conclusions  are 
to  be  reached.  In  general,  it  seems  preferable  to  reduce  such 


128  ELECTROLYSIS  SURVEYS 

readings  to  the  all-day  average  basis,  rather  than  to  the  operating- 
day  average  since  the  operating  day  varies  in  length  in  different 
cities. 

E.  EFFECT  OF  REVERSALS  OF  POLARITY 

Throughout  a  large  portion  of  the  territory  served  by  a  grounded 
railway  system,  it  will  be  found  that  the  potential  differences 
between  pipes  and  earth  frequently  reverse  in  direction,  the  pipes 
becoming  alternately  positive  and  negative  to  earth  with  periods 
varying  from  a  few  seconds  to  several  minutes  or  even  longer; 
and  special  consideration  has  to  be  given  to  measurements  in  such 
places  in  order  that  even  an  approximate  estimate  of  their  sig- 
nificance can  be  made.  In  general,  four  different  classes  of  con- 
ditions have  to  be  recognized  in  interpreting  these  measurements 
as  follows : 

1.  Polarity  of  Pipes  Always  the  Same. 

If  the  pipes  are  always  of  the  same  polarity,  as,  for  example, 
always  positive  to  surrounding  structures,  it  is,  of  course,  the 
arithmetical  average  value  that  should  be  used  in  judging  the 
significance  of  the  readings. 

2.  Polarity  of  Pipes  Changing  with  Long  Periods  of  Several  Hours. 

If  the  pipes  at  any  point  are  continuously  positive  for  a  period 
of  several  hours,  and  then  of  opposite  polarity  for  a  succeeding 
period  of  'some  hours,  a  condition  which  frequently  exists  in 
localities  where  a  substation  is  operated  during  only  a  portion 
of  the  day,  there  will  in  general,  be  relatively  very  little  protective 
effect  due  to  the  period  when  the  pipe  is  negative  or  neutral  to 
earth,  and  the  actual  corrosion  is  most  nearly  indicated  by  the 
arithmetical  average  value  of  the  voltage  or  currents  during  the 
hours  in  which  the  pipe  is  positive  to  earth,  this,  average,  of 
course,  being  reduced  to  the  twenty-four-hour  average  basis. 
Thus,  if  a  given  pipe  is  found  to  be  positive  to  the  earth  or  other 
neighboring  structures  by  a  given  amount  for  a  period  of  twelve 
hours,  and  either  negative  or  at  zero  potential  for  the  remaining 
twelve  hours  of  the  day,  the  actual  amount  of  corrosion  that  would 
occur  would  undoubtedly  be  nearly  equivalent  to  that  which 
would  result  if  the  potential  at  the  same  point  was  maintained 
half  as  great  for  the  full  twenty-four  hours. 

3.  Polarity  of  Pipes  Reversing  with  Periods  of  Only  a  Few  Minutes. 

Where  the  polarity  of  the  pipes  reverses  with  a  period  of  only  a 
few  minutes,  it  has  been  shown  by  extensive  experiments  that  the 


ELECTROLYSIS  SURVEYS  129 

corrosive  process  is  in  large  measure  reversible,  and  the  actual 
amount  of  corrosion  comes  more  nearly  being  proportional  to  the 
algebraic  average  of  the  applied  potential  than  it  is  to  the  arith- 
metical average  during  the  total  time  the  pipe  is  positive.  In 
all  cases,  therefore,  where  the  polarity  of  the  pipe  is  continuously 
reversing  and  the  period  of  reversal  does  not  exceed  five  or  ten 
minutes,  the  algebraic  average  of  the  voltages  or  currents  should 
be  given  far  greater  weight  than  the  arithmetical  average  values 
during  the  positive  period. 

4.  Polarity  of  Pipes  Reversing  with  Periods  of  From  Fifteen 
Minutes  to  One  Hour. 

Under  these  conditions,  neither  the  algebraic  nor  the  arith- 
metical average  of  the  applied  potential  or  current  flow  gives  an 
accurate  index  of  the  amount  of  corrosion.  For  the  shorter  period 
the  algebraic  average  comes  more  nearly  being  the  proper  criterion, 
while  as  the  period  increases  in  length  the  arithmetical  average 
tends  to  give  a  better  indication  of  the  extent  of  the  resulting 
corrosion.  However,  even  where  the  period  of  reversal  is  as  long 
as  one  hour,  the  corrosive  process  is,  under  most  conditions,  to  a 
considerable  extent  reversible  and  some  allowance  in  interpreting 
the  results  should  be  made. 

IV.  SELECTION  OF  INSTRUMENTS 

In  this  section  descriptions  are  given  of  the  apparatus  and 
tools  which  are  essentially  special  for  electrolysis  work.  The 
tools  ordinarily  used  for  handling  wires  and  making  good  contacts 
in  electrical  work  will  also  be  needed,  but  no  special  description 
or  listing  of  them  seems  to  be  necessary  in  this  place. 

A.  PORTABLE  MEASURING  INSTRUMENTS 

The  portable  measuring  instruments  required  in  electrolysis 
survey  work  include  voltmeters,  milli voltmeters,  and  ammeters. 
Separate  instruments  of  each  kind,  can -of  course,  be  carried,  but 
it  will  usually  be  found  more  convenient  to  employ  the  special 
portable  instruments  which  have  been  designed  particularly  for 
this  work.  Three  such  instruments  which  the  Weston  Electrical 
Instrument  Company  manufacture  for  this  class  of  work  are  as 
follows : 

Model  1,  combination  millivoltmeter  and  voltmeter,  has 
its  zero  in  the  center  of  the  scale,  and  reads  in  both  directions. 
Ranges  of  5,  50,  and  500  millivolts  and  of  5  and  50  volts  are 
convenient.  It  is  made  with  a  specially  high  resistance  of 


130  ELECTROLYSIS  SURVEYS 

from  500  to  600  ohms  per  volt  so  that  the  5  millivolt  range 
has  a  resistance  of  about  3  ohms.  These  high  resistances 
minimize  errors  due  to  resistances  of  leads  or  contacts.  For 
work  on  the  street,  a  dust-proof  case  should  be  specified. 
Ordinary  switchboard  shunts  provided  with  binding  posts 
and  adjusted  for  50  millivolts  may  be  used  to  make  this  instru- 
ment serve  as  an  ammeter.  Convenient  ranges  for  these 
shunts  in  electrolysis  work  are  5,  50,  and  500  amperes. 

Model  56,  combination  volt-ammeter  has  its  zero  in  the 
center  of  the  scale  and  reads  in  both  directions.  Ranges  of 
10,  50,  and  500  millivolts,  5  and  50  volts  and  up  to  100  am- 
peres are  convenient. 

Model  322,  millivoltmeter,  has  the  zero  at  the  left  of  the 
scale  and  a  full  scale  deflection  of  one  millivolt.  Owing  to 
the  low  range  and  extremely  light  movement  it  must  be  used 
with  a  great  deal  of  care.  It  is  useful  for  determining  very 
low  differences  of  potential  such  as  drops  along  short  sections 
of  pipe  or  feeder  for  determining  current  flow. 

The  center  scale  feature  referred  to  in  the  description  of  these 
instruments  is  an  important  one  in  electrolysis  work,  as  it  is  not 
always  possible  to  determine  in  advance  the  direction  of  current 
or  potential,  and  readings  may  also  vary  from  positive  to  negative 
values  during  the  making  of  observations  at  many  testing  points. 
When  simultaneous  readings  have  to  be  taken  at  two  or  more 
testing  points,  it  is  important  to  use  similar  instruments  at  all 
points.  If  dissimilar  instruments  are  used,  their  periods  may 
differ  and  with  the  fluctuating  voltages  and  currents  encountered 
i|i  much  of  this  work,  accurate  simultaneous  measurements 
cannot  be  made  unless  the  instruments  used  have  the  same  periods. 

B.    RECORDING  INSTRUMENTS 

Recording  measuring  instruments  are  usually  arranged  to  give 
24-hour  records  without  change  of  chart.  By  using  a  sensitive 
millivoltmeter  in  the  recording  instrument  and  providing  it  with 
a  number  of  voltage  ranges  as  well  as  with  suitable  shunts,  a 
single  instrument  can  be-  made  available  for  taking  all  of  the 
voltage  and  current  readings  required  in  electrolysis  work.  The 
type  of  Bristol  recording  instruments  used  for  electrolysis  work 
makes  a  record  upon  a  smoke-chart  which  has  to  be  treated  sub- 
sequently with  a  fixative  supplied  with  the  instrument.  The 
Bristol  instruments  are  regularly  made  with  a  clock  supplied  with 
a  changing  lever  so  that  the  disk  can  be  made  to  rotate  either  in 
one  hour  or  twenty-four  hours. 

The  Esterline  recorder  uses  ink  and  a  roll  chart  and  may  be 
obtained  with  a  large  range  in  chart  speeds.  This  is  particular  y 


ELECTROLYSIS  SURVEYS  131 

valuable  in  the  detailed  study  of  changes  which  take  place  during 
short  intervals  and  where  a  record  covering  more  than  one  day  is 
required.  The  clock  will  operate  for  a  week  with  one  winding. 
Several  other  manufacturers  make  portable  recorders  suitable  for 
some  electrolysis  measurements.  In  either  type  of  instrument, 
center  scale  zeros  should  be  called  for  so  that  variations  between 
positive  and  negative  values  will  be  recorded  on  the  chart. 

V.  RECORDS  AND  REPORTS 

A.     GENERAL  DISCUSSION 

Much  detailed  information  is  necessarily  gathered  in  the  course 
of  an  electrolysis  survey.  It  is  desirable  to  prepare  in  advance  of 
the  work  for  the  convenient  recording  of  these  data  upon  suitably 
arranged  testing  sheets,  which  either  have  upon  one  line  or  upon 
one  sheet,  as  may  be  necessary,  all  of  the  data  collected  at  any 
stated  testing  point  during  a  single  period  of  observation.  Several 
typical  data  sheets  prepared  for  recording  observations  made 
upon  piping  and  cable  systems  are  given  in  the  appendix  to  this 
report  as  suggestive  of  possible  arrangements  for  report  sheets.  The 
data  thus  collected  can  usually  be  best  arranged  for  study  if  they 
are  transferred  to  a  map  showing  the  system  or  systems  included 
in  the  tests,  and  indicated  thereon  either  in  numerical  form  or 
through  some  graphical  representation.  It  is  desirable  to  indicate 
positive  and  negative  relations  by  making  records  on  the  maps  in 
different  colors. 

Apart  from  the  data  obtained  through  observations  in  the  work 
of  the  electrolysis  survey,  the  records  obtained  relating  to  the 
systems  under  observation  should  include  the  following: 

B.     ELECTRIC  RAILWAYS 

1.  Maps  showing  locations  of  sources  of  power  supply,    tracks 
and  negative  feeders  and  other  connections  between  bus-bar  and 
track;  also    locations  of  positive  feeding  connections  to  trolley 
and  all  trolley  feeder  sections. 

2.  Information  regarding  magnitude  and  distribution  of  load 
shown  by  a  "spot  map"  of  the  railway  system. 

3.  Information  as  to  size  of  rails,  methods  of  bonding  and 
standards  of  bond  maintenance. 

4.  Information  as  to  any  direct  ground  connections  applied  to 
the  railway  return  system,  and  any  special  track  features  which 
may  affect  the  flow  of  stray  currents. 


132  ELECTROLYSIS  SURVEYS 

C.  PIPING  SYSTEMS 

1.  Maps  showing  all  main  pipe  lines  and  branches  (except  ser- 
vice connections)  and  sources  of  water,  gas,  etc.,  from  which  the 
piping  systems  are  supplied. 

2.  Information  as  to  sizes  of  pipes,  and  metals  of  which  they  are 
composed,  and  details  of  the  standard  methods  of  joining  main 
and  branch  line  pipe  sections. 

3.  Information  as  to  -method  of  joining  service  connections  to 
main  supply  pipes  including  metals  used  for  the  building  connec- 
tion pipes  and  the  depth  to  which  such  connections  are  buried. 

4.  Location  and  description  of  any  protective  devices  such  as 
insulating  joints;  also  any  drainage  connections  which  may  have 
been  made  a  part  of  the  piping  system. 

5.  Information  as  to  methods  of  attachment  and  construction 
employed  in  carrying  pipes  over  highway  or  railway  bridges  or 
under  water  courses,  swamps,  etc. 

D.  CABLE  SYSTEMS 

1.  Maps  showing  locations  of  all  conduit  routes  and  giving 
number  and  sizes  of  cables  in  place  therein  or  the  total  cross- 
section  of  lead  sheaths  expressed  in  equivalent  copper,  also  loca- 
tions of  power  stations,  sub-stations  or  other  centers  from  which 
cables  radiate.     Complete  data  on  bonding  practice  should  be 
secured. 

2.  Locations,  routes  and  sizes  of  all  drainage  connections  at- 
tached to  cable  systems,  also  locations  of  all  insulating  joints  in 
cable  systems,  of  any  junipers  which  may  be  run  to  establish  a 
metallic  circuit  across  an  insulated  gap  in  the  cable  system  and  of 
any  conductors  run  to  reinforce  the  carrying  capacity  of  the  cable 
system  for  stray  currents. 

3.  Information  as  to  methods  of  attachment  and  construction 
employed  in  carrying  cables  over  highway  or  railway  bridges  or 
under  water  courses,  swamps,  etc. 

E.    BRIDGES  AND  BUILDINGS 

1 .  Locations  of  structures  with  respect  to  electric  railways. 

2.  Information  as  to  methods  of  construction   employed  in 
carrying  electric  railways,  pipes  and  cables  across  bridges  and 
particularly  as  to  whether  any  of  these  other  structural  systems 
make  electrical  contact  with  the  metal  structure  of  the  bridge. 

F.     GENERAL  CONDITIONS 

1.  Maps  showing  locations  of  water  courses,  swamps,  and  other 
features  tending  to  produce  locally,  earth  of  high  unit  conductivity. 


ELECTROLYSIS  SURVEYS  133 

2.  Records  of  electrical  resistance  of  soil  samples  representative 
of  the  area. 

3.  Records  of  experience  obtained  in  the  use  of  different  metals 
for  pipes,  etc.,  in  the  soils  of  the  area. 

It  is  desirable  that  in  the  preparation  of  records  and  of  reports, 
consideration  be  given  to  the  necessity  of  their  perpetuation.  All 
records  which  will  be  of  permanent  value  in  connection  with  the 
continued  study  of  electrolysis  conditions  in  any  particular  area 
in  order  to  make  sure  that  injurious  changes  in  conditions  do  not 
occur,  should  be  prepared  in  a  permanent  form  capable  of  with- 
standing considerable  handling. 

VI.  TABLES 

The  tables  in  the  appendix  are  to  be  used  for  calculating  the 
current  flow  in  different  kinds  and  sizes  of  pipes  from  the  measure- 
ment of  the  millivolt  drop  on  a  definite  length  of  pipe.  These 
tables  were  prepared  by  the  U.  S.  Bureau  of  Standards  from  a 
large  amount  of  test  data  taken  on  representative  specimens  of 
pipe  from  a  number  of  different  manufacturers. 

The  figures  for  wrought  iron  pipes  represent  the  results  of  tests 
made  on  86  separate  specimens  of  pipe.  Those  for  steel  pipe  are 
based  on  tests  of  64  specimens,  and  those  for  cast  iron  are  based 
on  test  data  from  22  specimens  of  pipe  from  a  number  of  different 
foundries. 

The  tables  for  lead  pipe  are  based  on  test  data  taken  on  27 
specimens  ranging  from  one-fourth  to  two  inches  in  diameter, 
all  of  which,  however,  were  obtained  from  one  manufacturer.  It 
is  believed,  however,  that  these  figures  can  be  used  for  all  lead 
service  pipes  with  sufficient  accuracy  for  most  practical  purposes. 

These  tests  showed  that  the  resistance  of  cast  iron,  wrought 
iron,  and  steel  pipes  can  be  estimated  from  these  tables  with  an 
accuracy  of  at  least  10  per  cent,  and  in  most  cases  the  results  will 
be  even  better  than  this.  The  tests  showed  an  average  resistivity 
for  steel  pipe  of  215.8  microhms  per  pound-foot,  for  wrought  iron 
pipe  209.3  microhms  per  pound-foot,  and  for  cast  iron  the  figure 
is  1,227  microhms  per  pound-foot.  These  average  values  have 
been  used  in  the  calculation  of  the  tables. 

Tables  for  lead  sheathed  cables  have  not  been  included  in  this 
report,  owing  to  the  large  number  of  different  sizes  and  thicknesses 
of  sheaths  used  for  signal  and  power  cables,  as  well  as  a  variation 
in  resistivity  with  different  sheath  compositions. 


CHAPTER  4 

EUROPEAN   PRACTICE 
A.     GENERAL 

In  the  study  of  the  practice  followed  in  European  countries  for 
handling  the  problem  of  electrolysis,  it  has  appeared  impossible 
to  secure  reliable  and  satisfactory  information  merely  by  cor- 
respondence and  consultation  of  published  reports  and  regulations. 
Moreover,  the  several  independent  reports  made  by  American 
investigators  before  the  foundation  of  the  American  Committee, 
were  made  from  the  standpoint  of  some  special  industry  rather 
than  from  the  broad  and  comprehensive  viewpoint  of  this  Com- 
mittee. Under  these  circumstances  the  necessity  for  an  inde- 
pendent personal  investigation  was  evident. 

The  Chairman  of  this  sub-committee,  after  consultation  with 
its  members  and  with  the  general  Chairman,  decided  to  visit 
several  European  countries  during  the  summer  of  1914.  Informa- 
tion concerning  important  foreign  cities  and  authorities,  and 
papers,  suggestions  and  references  were  obtained  from  Mr.  H.  S. 
Warren  and  the  late  Prof.  Albert  F.  Ganz.  Also  the  officials  of 
the  Bureau  of  Standards  were  consulted  when  the  field  of  inquiry 
and  special  points  to  be  looked  after  were  carefully  discussed. 
An  effort  to  have  the  Bureau  of  Standards  appoint  a  representative 
to  join  trie  party  failed  on  account  of  their  extensive  engagements. 
However,  the  party  included  an  engineer  thoroughly  conversant 
with  electrolysis  measurements  and  surveys. 

The  visiting  Committee  spent  June  and  July  in  its  investigation, 
covering  Germany,  Italy,  France,  and  England.  In  each  country 
an  effort  was  made  to  take  measurements  and  to  collect  data  and 
surveys,  also  to  interview  the  most  prominent  people  in  each  of  the 
different  interests  affected  by  the  problem  of  electrolysis.  In 
each  case  extended  conferences  were  held  with  the  engineers  most 
familiar  with  the  problem  and  its  details,  either  in  their  capacity 
of  specialized  consulting  engineers,  or  as  officials  of  corporations 
or  public  authorities  directly  concerned  in  the  surveys,  disputes, 
or  administrative  measures  relating  to  electrolysis. 

After  this  investigation  of  1914,  the  conditions  which  existed 

during  the  War  and  later,  made  it  impossible  to  collect  any  further 

information  until  the  winter  of  1920-21,  and  even    then    only 

fragmentary  reports  of  later  developments  were  obtained  from 

134 


EUROPEAN  PRACTICE  135 

Great  Britain  alone.  However,  it  is  believed  that  the  same  cir- 
cumstances have  retarded  development  so  that  the  conditions 
observed  in  1914  correspond  substantially  with  those  existing  at 
the  present  time.  It  should  be  borne  in  mind,  however,  that 
references  in  this  report  to  the  current  status  of  committees  or 
commissions,  and  of  legislation  or  litigation,  will  unless  otherwise 
noted,  refer  to  the  ;ummer  of  1914. 

The  results  of  the  Sub-Committee's  investigations  are  summar- 
ized in  the  paragraphs  immediately  following,  classified  by  prin- 
cipal topics.  This  is  followed  by  statistical  information,  details  of 
design  and  operation,  and  rules  and  regulations  in  effect  in  different 
European  countries. 

B.     LAWS  AND  REGULATIONS 
1.  Germany. 

There  are  no  laws  specifically  relating  to  electrolysis,  and  so 
far  as  could  be  ascertained,  there  are  no  local  ordinances  dealing 
with  this  subject.  The  common  law  of  most  of  the  states  pre- 
scribes that  all  of  the  conditions  under  which  a  corporation  is  to 
operate  must  be  contained  in  the  original  .grant  and  any  later 
grants  for  extensions.  The  law  requires  that  due  publicity  be 
given  to  any  request  for  a  franchise  or  for  extensions  of  lines,  so 
as  to  afford  all  parties  who  may  be  affected  an  opportunity  to 
place  on  record  any  limitation  they  may  desire  to  propose,  or  to 
request  provisions  concerning  possible  damage,  before  the  conces- 
sion is  granted  to  the  applicant.  Hence,  a  pipe  owning  company 
organized  subsequently  to  the  existence  of  an  electric  railway  is 
held  to  have  assumed  the  risks  existing  at  the  time  of  its  organiza- 
tion, and  it  therefore  cannot  claim  damages  from  this  railway  on 
account  of  electrolysis  unless  the  original  franchise  to  the  railway 
contained  a  clause  regarding  such  damage. 

The  foregoing  applies  to  private  corporations.  Municipal 
corporations,  on  the  other  hand,  do  not  assume  the  legal  obligation 
to  protect  existing  systems  against  the  effects  of  electrolysis. 
In  such  cases,  pipe  owning  companies  already  in  existence  are 
deprived  of  the  privilege  of  demanding  that  protection  against 
possible  future  damage  which  would  be  accorded  them  in  the 
case  of  a  new  privately  owned  railway  company. 

Municipalities,  however,  for  their  own  new  railway  construction 
as  well  as  for  new  extensions  of  the  railways  of  private  companies, 
always  prescribe  that  they  be  constructed  and  operated  in  accord- 
ance with  existing  technical  standards.  The  recommendatioias 


136  •  EUROPEAN  PRACTICE 

of  the  German  Earth  Current  Commission  are  recognized  as  the 
existing  technical  standards  in  matters  relating  to  electrolysis 
and  in  this  manner  they  have  assumed  almost  the  importance 
of  law.  These  regulations  are  being  generally  incorporated  in 
contracts  for  new  enterprises  or  extensions,  and  in  such  cases 
they  do  substantially  attain  the  force  of  law. 

(a)  Commission  Recommendations.  The  work  of  the  German 
Earth  Current  Commission  is  described  in  detail  in  another  place, 
and  a  translation  of  the  complete  text  of  its  recommendations  is 
given  later.  The  recommendations  of  the  Commission  were 
adopted  by  the  German  Electrotechnical  Society  in  1910.  In  ab- 
stract the  recommendations  prescribe  the  following : 

In  large  cities,  and  in  general  in  urban  networks  and  for  a 
distance  of  2  km.  (1.24  miles)  beyond,  the  overall  rail  drop  is 
limited  to  2.5  volts.  Outside  of  this  zone,  and  in  general  in  small 
places  or  for  single  lines,  the  potential  gradient  is  limited  to  1  volt 
per  km.  (1.6  volts  per  mile).  Exceptions  are  made  for  roads 
operating  only  a  few  hours  in  the  day.  Bonds  must  not  increase 
the  resistance  of  tracks  over  20  per  cent;  they  must  be  tested 
yearly,  and  when  a  bond  shows  a  resistance  higher  than  ten 
meters  (11  yards)  of  rail  it  must  be  repaired.  Connections  to 
pipes  are  prohibited.  Bare  return  feeders  are  not  allowed. 
Pilot  wires  are  prescribed.  The  voltage  limits  given  are  inter- 
preted to  be  the  average  for  the  entire  daily  period  of  operation, 
usually  18  to  20  hours  in  24  hours.  If  measurements  are  not 
actually  taken  over  the  entire  period  they  are  corrected  to  obtain 
a  figure  corresponding  to  this  average. 

2.  Italy. 

The  Government  has  not  enacted  any  law  affecting  the  operation 
of  electric  railways  in  relation  to  electrolysis  problems,  nor  has 
any  municipality  issued  regulations  on  the  subject. 

3.  France. 

Regulation  in  France  is  based  on  a  Ministerial  decree  of 
March  21,  1911,  establishing  the  technical  conditions  which 
electrical  distribution  systems  must  satisfy  in  order  to  conform 
to  the  Law  of  June  15,  1906.  A  translation  of  the  text  of  this 
decree  is  given  later.  Briefly  the  requirements  are : 

That  the  maximum  voltage  drop  in  rail  returns  of  electric 
tramways  shall  not  exceed  one  volt  per  kilometer  (1.6  volts  per 
mile) ;  an  exception  is  made  for  locations  where  metallic  masses, 
such  as  pipe  networks,  do  not  exist.  Bonds  must  be  kept  in  the 


EUROPEAN  PRACTICE  137 

best  possible  condition;  the  resistance  of  a  bond  must  not  be 
greater  than  ten  meters  (11  yards)  of  normal  rail.  Return 
feeders  must  be  insulated.  Periodic  tests  must  be  made  and 
recorded  on  a  register  subject  to  inspection  by  the  control  service. 
No  definition  is  given  of  the  time  element  in  the  measurement 
of  maximum  drop,  except  that  it  is  stated  that  it  must  be  the 
average  for  the  normal  schedule. 

4.  Spain. 

A  translation  of  sections  of  the  Law  of  March  23,  1900,  relating 
to  electric  railway  return  circuits  is  given  later.  Briefly,  this 
law  requires  the  overall  voltage  not  to  exceed  seven  volts,  specifies 
bonding  and  cross-bonding,  and  where  necessary  reinforcements 
of  rail  conductivity. 

5.  Great  Britain. 

Control  of  electrolysis  matters  in  Great  Britain  is  obtained 
through  regulations  made  by  the  Board  of  Trade  under  the 
provisions  of  special  Tramways  Acts  or  Light  Railway  Orders 
authorizing  "lines"  on  public  roads;  for  regulating  the  use  of 
electric  power;  for  preventing  fusion  or  injurious  electrolytic 
action  of  or  on  gas  or  water  pipes  or  other  metallic  pipes,  structures, 
or  substances ;  and  for  minimizing,  as  far  as  it  is  reasonably  prac- 
ticable injurious  interference  with  the  electric  wires,  lines,  and 
apparatus  of  parties  other  than  the  railway  company,  and  the 
current  therein,  whether  such  lines  do  or  do  not  use  the  earth  as 
a  return. 

The  Board  of  Trade  Regulations  were  first  made  in  March, 
1894;  they  have  been  revised  from  time  to  time,  the  last  revision 
having  been  made  in  September,  1912.  The  full  text  of  the  Regula- 
tions is  given  in  a  following  section  of  this  report.  In  abstract, 
the  regulations  prescribe  that  the  overall  rail  drop  shall  not 
exceed  seven  volts,  and  there  are  also  clauses  concerning  track 
leakage,  the  measurement  of  these  quantities,  etc.  The  regula- 
tions also  provide  for  circular  returns  to  be  made  upon  the  call 
of  the  proper  authorities. 

The  Board  of  Trade  makes  inspections  on  its  own  initiative 
because  it  is  responsible  for  its  rules,  which  have  substantially 
the  force  of  law;  it  also  investigates  complaints.  There  are  no 
regular  inspections  on  account  of  the  lack  of  a  proper  appropria- 
tion. Most  of  its  information  is  obtained  from  the  returns;  the 
latest  call  for  a  return  was  issued  in  1906. 

The  overall  voltage  is  defined,  in  practice,  as  an  average  for 


138  EUROPEAN  PRACTICE 

about  twenty  minutes  at  peak  load.  This  "average"  is  obtained 
as  the  mean  between  the  average  of  the  maxima  during  the  period 
(disregarding  unusually  high  swings)  and  the  actual  average  of  all 
measurements.  This  quantity  is  usually  obtained  in  practice 
from  inspection  of  recording  instrument  charts. 

There  are  no  local  ordinances  which  have  the  effect  of  modifying 
the  Board  of  Trade  Regulations.  Pipe  owning  companies  cannot 
recover  damages  in  case  corrosion  occurs  where  the  Regulations 
are  complied  with.  This  has  led  to  numerous  applications  to 
Parliament  for  special  statutory  orders  fixing  responsibility  for 
damage,  or  special  clauses  of  like  import  in  Acts  granting  powers 
to  electric  railway  undertakings.  Most  of  these  have  been  re- 
fused, but  some  have  been  granted. 

It  is  generally  admitted  that  the  Board  of  Trade  Regulations, 
as  originally  drawn,  were  empirical,  and  that  they  might  be  re- 
modeled with  advantage ;  but  since  the  only  feature  of  the  regula- 
tions actually  rigidly  enforced,  namely,  the  limit  for  overall 
rail  drop,  results  in  substantial  immunity,  the  great  difficulty 
attending  revision  has  not  seemed  to  be  justified. 

Railway  electrifications,  as  distinguished  from  tramways,  do 
not  come  under  the  above  regulations  unless  it  is  especially  pro- 
vided in  the  Parliamentary  Act  authorizing  the  electrification. 
Recent  advices  indicate  that  railway  electrifications  generally 
have  not  been  brought  under  the  Regulations. 

C.  CONSTRUCTION  CHARACTERISTICS 

General  types  of  construction  for  electric  railways  and  pipe 
or  cable  systems  and  special  features  characterizing  such  systems 
in  the  various  countries  visited,  are  summarized  here.  Details 
of  construction  and  statistical  tables  are  given  in  Figs.  25  to  31, 
and  Tables  7  and  8. 

1.  General. 

In  large  cities  the  tramways  are  supplied  from  a  number  of 
substations,  as  in  the  municipal  systems  of  Glasgow  and  Man- 
chester. In  Berlin,  particularly  the  railway  system  is  supplied 
from  a  great  number  of  combination  light  and  railway  substations 
feeding  limited  districts  entailing  relatively  small  positive  line 
drop  of  potential.  In  England,  average  feeding  distances  are 
said  to  be  from  two  to  three  miles  (3  to  5  km). 

The  ordinary  single  overhead  trolley  with  the  running  rails 
used  as  some  part  of  the  return  circuit,  is  predominantly  used  in 


EUROPEAN  PRACTICE 


139 


all  of  the  countries  visited.     Special  features  of  the  return  circuit 
are  discussed  under  appropriate  headings  below. 

The  gas  and  water  piping  systems  in  all  of  the  countries  visited 

German  Tramway  Rails 


Rillenschiene 
Phonix  Profll    land  la 
.42.6    and  -45/7 
&eo    end  91.9 


Viqnolschiene 
Special  Pro-file  for  Tramway 


(a)  Rilleoscbiene  wiih  Foot 
Rsh    Plate 


(b)  Haarman  a  piece  Pail 


^ 

1 

% 

II                           l'j 

0 

o 

o     o  -  ii  o     o  ji  o     o 

O                       ij                 j;                      O 

(c)and(d)haarw)an  2-piece   Rail 


Fig.  25. 

did  not  present  any  features  differentiating  them  from  piping 
systems  in  America,  so  far  as  the  electrolysis  problem  is  con- 
cerned. In  general,  pipes  are  laid  in  somewhat  more  shallow 
trenches  than  in  our  northern  states,  and  interconnection  between 


140 


EUROPEAN  PRACTICE 


gas  and  water  systems  for  heating  devices  seem  to  be  less  common 
than  in  America. 

2.  Rails. 

In  Germany,  the  common  rail  weights  are  50-60  kg.  per  meter 

BRITISH  TRAMWAY  RAILS 


r 


Standard  prior  to   1908 
t 


\      Present  Standard  "Brit  Stand." N?  4 
Bessemer  Steel   100- 105  Ibs  per  yd 
Fish  plates  2' long  635  Ibsper pair 


-inner  fish 
plate  2'  long 
26  Its 


Outer  fish 

plate  2'  long 

305  Ibs 


Straight  track,  110  Ibs  per  yard 
"British  Standard"  Section  N?  5 


Curbed  track,  116  Ibs.  per  yard 
"°ritish  Standard"  Section  N?5c. 


Fig.  26. 


(101-121  Ibs.  per  yard)  for  tramways,  and  30-40  kg.  per  meter 
(60-81  Ibs.  per  yard)  for  interurban  lines.  In  France  the  ordinary 
rail  weights  are  46  to  51  kg.  per  meter  (93-103  Ibs.  per  yard). 
In  England  rail  weights  vary  from  70  to  100  Ibs.  per  yard  (34.7- 


EUROPEAN  PRACTICE 


141 


49.6  kg.  per  meter)  in  the  majority  of  cases.      (See  Figures  25, 
26,  and  27.) 

3.  Rail  Bonds. 

Solid  copper  pin  type  bonds,  usually  1  meter  (3.3  ft.)  long, 

PAIL  WEIGHT  DATA 


3000 


«2000 


1000 


1000 


750 


500 


250 


40 


tao 


Gf  R  Mi  k  M  V 


Classified  by  Rail  "types 
Tptall 


Rillenschien*  •  5902  Km.'366dMi 
Viqnolschiene  =  1020  Km  634Mi 
Wecfcseb+eg  .  7l4Kir»-444Mi 


Rilldnschi 


10 


40 


50 


I    I 

UNITED 


Classi 


MTEP    KINGDOM 
fiedby  Track  Gauges 

*" 


Totals 


'#  t  \\i  and  3'  1rack  OfltfM  *     29. 6  miles  4a6to 
3V     »        ••      -\QS66     ••  1700^)  - 


4'l 
5'3<T 


*Not  ploited 


293  8  -  47Z.7 
404.fi  6513 
1039.4  —^-1672.4- 
114.2  "  163-7 


Large  Systems  other  1han  Standan 
.  Cork  -•  15  miles  -2'  ((£  qauqe . 

Birmingham  Corp.   16  7  miles 

Bradford-- 100 miles -4* 


ClasdoW  - 196-5  mite5 
Dublin  *IOd  miles  -5f 


_1 - ^ I 

J  1"^ 

40  60  80 


166 


124. 


(603 


401 


100 


IZO 


Fig.  27. 

are  most  commonly  used  in  Germany  and  France.  The  Metro- 
politan System,  in  Paris,  places  the  bonds  under  the  base  flange 
of  the  rail.  In  England,  solid  copper  pin  type  bonds',  protected 


142 


EUROPEAN  PRACTICE 


bonds  inside  of  fish  plates,  and  other  types  familiar  in  America, 
are  generally  used.     (See  Figure  28,  and  Table  7.) 

In  Germany  Thermit  welds  are  used  to  some  extent,  and  are  be- 
coming more  common.     In  France  the  rails  of  the  Cie  de  Omnibus 

TYPICAL  RAIL.  BONOS  -  UNITED  KINGDOM 


MANCHESTER 
(Standard) 


GLASGO  w 

(Standard) 


Fig.  28. 


Thomson-Houston  are  welded.  In  England  Thermit  welds  have 
been  used  very  extensively,  giving  good  results  electrically,  but 
having  short  life  due  to  mechanical  weakness  where  traffic  is  heavy. 
A  type  of  electrically  welded  continuous  rail,  very  extensively  used 


EUROPEAN  PRACTICE 


143 


TABLE  7 
RAIL  BONDING,  UNITED  KINGDOM 


No.  of 
Undertakings 

Miles  of 
Single  track 

Per  cent 
of  total 
(miles) 

Copper  Bonds. 

Solid  copper,  type  not  specified.  .  . 
Flexible  copper,  type  not  specified. 
Crown  —  3/0  and  4/0 

46 
9 
20 

560.0 
176.0 
321  0 

Neptune  4/0 

19 

229  2 

Chicago 

8 

71  3 

Forest  City 

5 

37  2 

Misc.  and  type  not  specified  

15 

406.8 

Total,  copper  bonds  only  
Welded  Rails,  Etc. 
Continuous  rails,  type  not  speci- 
fied          

122 
1 

1801.5 
17  0 

47.3 

Yalk  cast  weld  
Thermit  
Thermit  and  Yalk  
Thermit  and  Tudor  
Thermit  and  Oxy-  Acetylene  

1 
3 
1 
1 

1 

20.0 
61.6 
15.9 
28.0 
18.0 



Total,  entirely  welded  
Partially  Welded. 
Copper  and  Thermit  
Copper  and  other  welded  joints  .  . 

8 

31 

5 

160.5 

1312.4 
377.3 

4.2 

Total   partially  welded.    .  . 

36 

1689  7 

44  3 

Plastic  Bonds,  Etc. 

Plastic  bonds  and  copper  

3 

147  5 

Plastic  bonds  and  Thermit  

1 

12.3 

4 

159.8 

4.2 

in  Leeds,  and  to  an  increasing  extent  in  Manchester  and  Glasgow, 
is  giving  excellent  results,  being  mechanically  strong  and  providing 
good  electrical  conductivity. 

4.  Cross  Bonds. 

In  Germany,  cross  bonds  are  used  about  every  ten  rails,  i.e., 
every  100  meters  (109  yards).  In  France  they  are  placed  every 
50  to  100  meters  (55  to  109  yards)  and  have  the  same  area  as  the 
small  rail-bonds.  In  England  cross  bonds  are  generally  every 
forty  yards  (36.6  meters)  and  they  have  the  same  area  as  the 
rail-bonds.  (See  Fig.  29). 

5.  Roadbed  Construction. 

The  authorities  consulted  in  Germany  were  of  the  opinion  that 


144 


EUROPEAN  PRACTICE 


the  roadbed  constructions  used  did  not  tend  to  affect  a  reduction 
of  leakage  from  tracks;  a  similar  opinion  was  held  in  England. 
The  types  of  construction  referred  to  were  those  illustrated  in 
Figs.  30  and  31. 


CROSS-BONDING  DETAFLS,  ETC  -  UNITED  KINGDOM 

GLASGOW 

Standard  Cross-Bonding 


Single  Cross  Bondr* 


Rail 


40  yards  (2  rail  lengths) 


Method  of  connecting 
one  return  cable  to 
track 

LONDON 
LCC  Return  Feeder  Connections 


Rail 


4-NeOOGO  B&S  Bonds 

per  terminal,  about 

34"  long,. 


Rail 


Bond  Terminal 
clamped  and 
soldered 


Rail 


Bare  Cable-* 


Rail 


Lead  Sleeve 

Method  of  connecting 
two  return  cables  to 
track  at  same  point. 

Fig.  29. 


LC.  Cable 


A  later  English  report  (1920)  emphasizes  the  importance  of 
thorough  drainage,  as  provided  by  broken  stone  foundations,  as  a 
means  for  reducing  leakage  current.  The  same  report  gives  the 
following  as  good  average  leakage  figures  for  tramway  rails  in 


EUROPEAN  PRACTICE 


145 


146 


EUROPEAN  PRACTICE 


Length  of  Section 

Feet 

Meters 

Per  cent  Leakage  Current 

3,000 

914 

2.5 

4,200 

1,280 

5.0 

6,000 

1,829 

10.0 

7,400 

2,256 

15.0 

8,600 

2,621 

20.0 

9,500 

2,896 

25.0 

TRACK  CONSTRUCTION  AND  RAILS  -  GERMANY 


Typical  Construction  for  paved  street 


STRASSBURG 
Haarman.  3  piece  Rail,  and  foot  plate 


Fig.  31. 

direct  contact  with  soil.  The  table  is  based  on  equal  unit  loading 
for  various  lengths  of  section. 

Leakage  current  is  proportional  to  the  square  of  the  length,  and 
direcfty  proportional  to  overall  voltage. 

The  report  also  states  that  tests  on  railway  tracks  laid  on 


EUROPEAN  PRACTICE  147 

wooden  sleepers  with  broken  stone  ballast  show  about  25  per  cent 
of  the  leakage  for  tramway  rails. 

Tests  made  in  Strassburg  indicated  that  leakage  currents  were 
fifty  per  cent  greater  in  summer  than  in  winter  when  the  ground 
was  frozen.  In  snow  storms,  however,  the  winter  leakage  currents 
were  increased  as  the  cars  were  using  more  current. 

6.  Feeders. 

Insulated  return  feeders  are  used  almost  universally  in  Germany. 
In  Berlin  and  Hamburg  these  return  feeders  are  of  the  same  num- 
ber and  size  as  the  positive  feeders,  but  generally  in  other  towns 
the  return  feeders  are  of  smaller  cross-section.  Separate  feeders 
are  generally  used,  but  not  exclusively,  as  feeders  with  resistance 
taps  are  used  in  some  cases.  Formerly  there  were  cases  of 
feeders  tapping  at  several  points  but  important  cases  have  been 
corrected  by  the  insertion  of  resistances.  No  design  data  for 
feeder  resistances  were  obtained.  The  Hamburg  installation  of 
insulated  feeders  was  made  prior  to  the  formation  of  the  German 
Earth  Current  Commission.  It  gave  valuable  information  in 
guiding  the  recommendations  of  the  Commission. 

Return  feeders  are  not  used  for  tramways  in  Italy;  in  large 
installations  bare  returns  are  generally  used.  In  France  most 
tramways  have  but  one  feeding  point  to  the  rails.  Insulated 
return  feeders  are  used  for  the  conduit  tramways  in  Paris,  but 
little  elsewhere. 

In  England  insulated  return  feeders  are  used  wherever  they  are 
necessary  to  bring  the  rail  drop  within  the  B.  O.  T.  regulations; 
separate  feeders  are  generally  used.  There  is  very  little  overhead 
feeder  line  construction  in  Germany,  and  almost  none  in  England. 

In  Germany  insulated  negative  feeder  systems  have  been  care- 
fully calculated  in  recent  installations.  In  England  they  are 
calculated  only  in  the  larger,  well  supervised  systems;  elsewhere 
they  are  installed  by  "cut-and-try"  methods.  The  same  grade 
of  insulation  is  usually  provided  for  both  positive  and  negative 
feeders.  The  distinction  between  copper  which  merely  parallels 
the  rails,  and  feeders  which  are  intended  to  reduce  overall  poten- 
tials by  maintaining  equipotential  points  in  the  rail  network,  is 
clearly  understood  in  Germany  and  England. 

Recent  reports  concerning  heavy  railway  electrifications  in 
England  indicate  that  insulated  return  feeders  are  not  generally 
used  on  such  systems,  possibly  because  they  are  not  limited  to  the 
overall  voltages  of  the  Tramway  regulations.  The  usual  practice 


148  EUROPEAN  PRACTICE 

is  to  locate  the  substation  close  to  the  track  and  to  connect  the 
negative  bus  to  the  rails  with  short,  heavy,  cables.  In  general  the 
negative  busbars  of  substations  supplying  electrified  railw  lys  are 
not  deliberately  earthed,  by  means  of  earth  plates,  connections  to 
piping  systems,  or  otherwise.  Two  railway  electrifications  and 
some  of  the  underground  railways  in  the  Metropolitan  District 
provide  an  insulated  fourth  rail  for  return  current,  leaving  the 
running  rails  free  for  signaling. 

7.  Negative  Boosters. 

Negative  boosters  are  used  in  many  places.  In  Germany  the 
general  practice  is  not  to  use  them  but  they  are  much  more  ex- 
tensively used  in  England  (See  Table  8)  where  they  are  generally 
found  in  the  larger  systems.  They  are  considered  more  econom- 
ical than  resistances  in  the  return  feeders  and  also  better  for  regu- 
lation where  the  load  centers  shift.  In  one  large  .city  their  use 
was  discontinued  after  they  had  been  in  operation  for  some  time. 
The  Tramways  of  Danzig,  in  Germany,  operated  by  a  private 
company  and  having  a  maximum  load  of  600  kw.,  has  used 
boosters  since  1906. 

Boosters  are  very  little  used  in  France,  the  only  system  found 
to  be  equipped  with  them  was  that  of  the  Cie  des  Tramways  de 
Paris  et  du  Dept.  de  la  Seine. 

TABLE  8 
USE  OF  NEGATIVE  BOOSTERS,  UNITED  KINGDOM 


Number 

Miles  of 
single  track 

Total  number  of  undertakings  
Number  of  undertakings  using  negative  boosters. 
Per  cent  using  negative  boosters  

183 
39 

21.3% 

3,835.0 
1,152.0 
30.0% 

Relation  Between  Booster  Capacity  and  Plant  Capacity 

Average,  for  25  cases:  Booster  Capacity — 3.9%  of  plant  capacity. 

Highest —    9  %  for  plant  of     500  kw.  capacity. 

12  %  for  plant  of     800  kw.  capacity. 

Lowest — 0.8  %  for  plant  of  5,725  kw.  capacity. 

0.9  %  for  plant  of  3,500  kw.  capacity. 

The  use  of  a  negative  booster  in  the  return  circuit  of  an  electri- 
fied railway  is  mentioned  in  a  recent  report.  The  booster  was 
installed  for  the  purpose  of  relieving  load  on  a  section  of  the  line , 


EUROPEAN  PRACTICE 


149 


a  cable  being  run  out  from  the  booster  to  the  section  to  be  relieved. 
The  effects  are  reported  as  follows: 


Volts  drop  on  Section 

Section  tested 

Per  cent  Decrease  in 
Drop  due  to  Booster 

Booster  on 

Booster  off 

1st  Section  

5.6 

6.75 

17.0 

2d  Section  

5.75 

6.9 

16.7 

3d  Section  

3.91 

6.12 

36.3 

The  booster  was  not  continued  in  service  because  it  was  not 
effective  in  relieving  the  second  section. 

8.  Double  Trolley. 

The  double  trolley  system  is  not  in  general  use  in  any  of  the 
countries  visited.  One  or  two  very  special  cases  near  Laboratories 
in  Germany,  the  district  within  two  or  three  miles,  (three  to  five 
kilometers)  of  the  Greenwich  Observatory,  and  some  conduit 
tramways  of  the  London  County  Council  System  and  in  Paris 
were  the  only  cases  noted.  The  double  trolley  is  also  used  in 
connection  with  a  few  miles  of  rail  less  trolley  in  England. 

9.  Three-wire  System. 

The  three-wire  system  has  been  applied  to  electric  railways  in 
a  few  cases  in  Germany.  In  each  case  the  distribution  of  load 
between  polarities  was  by  districts,  that  is,  certain  entire  sections 
have  the  trolley  wire  negative.  Under  these  conditions  the 
systems  may  become  considerably  unbalanced. 

In  France,  the  Chem  de  Per  Nord-Sud,  in  Paris,  employs  a 
three-wire  system  with  two  motors  per  car,  positive  and  negative, 
the  running  rails  acting  as  a  grounded  neutral  while  the  supply 
is  provided  by  a  third  rail  and  one  trolley  wire. 

The  three-wire  system  has  not  been  applied  to  tramways  in 
England.  The  City  and  South  London  Underground  Railway 
employed  it,  but  this  was  to  be  discontinued  following  consolida- 
tion with  other  systems. 

10.  Negative  Trolley. 

The  trolley  wire  was  originally  made  negative  in  Nuremberg, 
and  in  St.  Gall,  Switzerland.  The  scheme  has  been  abandoned 
in  both  places.  This  connection  has  not  been  used  for  tramways 
in  Italy,  France  or  England. 


150  EUROPEAN  PRACTICE 

11.  Pilot  Wires. 

In  Germany  permanent  means  for  measuring  overall  potentials 
are  very  generally  provided,  but  the  methods  of  doing  this  vary 
widely.  Pilot  wires  are  usually  provided  for  new  installations  in 
France. 

In  England  pilot  wires  are  universally  used  in  connection  with 
recording  instruments.  The  practice  varies  widely,  but  the  most 
common  method  employs  No.  14  or  No.  16  gauge  wires  laid  with 
the  main  cables,  and  extended  beyond  them. 

12.  Bond  Testing. 

Bond  testing  is  generally  done  in  Germany  on  some  systematic 
basis,  more  often  annually,  but  in  some  large  systems  semi- 
annually.  The  bond-testing  devices  are  generally  of  the  three 
contact  type  with  differential  galvanometer.  Some  of  these  are 
said  to  be  undesirable  on  account  of  the  form  of  the  contact,  others 
because  the  rail  points  span  too  short  a  length,  or  on  account 
of  the  type  of  galvanometer  employed,  etc.  In  England  it  is 
stated  that  there  is  practically  no  systematic  bond  testing,  except 
in  the  large  well  supervised  systems. 

13.  Pipes  and  Pipe  Joints. 

Cast-iron  pipes  in  England  and  Germany  are  generally  of  the 
bell  and  spigot  type  with  lead  calked  joints.  In  Germany  flanged 
joints  are  frequently  used  for  special  fittings,  valves,  tees  and 
hydrant  taps  for  water  mains.  Cast-iron  pipes  are  little  used  in 
France;  pipe  joints  are  either  lead  calked  bell  and  spigot,  or  in 
large  pipes  flanged,  with  rubber  gaskets.  Insulating  joints  are 
not  used,  except  that  in  England  it  is  said  that  they  are  occasion- 
ally used  for  water  pipes  in  special  cases. 

14.  Depth  of  Pipes  Below  Surface. 

In  Germany, 'gas  pipes  are  generally  laid  0.8  to  1  meter  (2.6  to 
3.3  feet)  and  water  pipes  1  to  1.5  meters  (3.3  to  5  ft.)  below  the 
surface.  In  France,  gas  pipes  are  laid  where  possible  0.6  meter 
(2.0  feet)  below  the  surface,  L.  T.  cables  0.7  meter  (2.3  feet)  and 
H.  T.  cables  1.3  meters  (4.3  feet).  In  England  1  foot  (0.3  meter) 
is  said  to  be  dangerous,  2  feet  (0.6  meter)  was  given  as  an  average 
by  one  authority,  and  2.5  to  5  feet  (0.8  to  1.5  meters)  by  another. 
In  all  cases  the  above  depths  are  only  typical,  the  practice  varies 
widely. 


EUROPEAN  PRACTICE  151 

15.  Mains  on  Both  Sides  of  Streets. 

In  Germany,  France,  and  England  mains  are  laid  on  both  sides 
of  the  principal  streets;  in  Paris,  for  streets  wider  than  14  meters 
(46  feet);  also  in  streets  with  wood  or  asphalt  pavements,  and 
generally  in  the  larger  towns.  In  narrow  streets  or  unimportant 
places  one  main  is  used.  In  Paris  the  pipes  for  water  are  located 
in  the  sewers,  not  in  direct  contact  with  soil,  and  remote  from 
trouble. 

16.  Insulating  Coverings  for  Pipes. 

In  Germany  it  is  held  that  insulating  coverings  do  not  afford 
protection  against  electrolysis,  as  their  effect  is  merely  to  concen- 
trate escaping  stray  currents  since  perfect  coverings  cannot  be 
maintained.  They  should  only  be  used  where  it  is  desired  to 
protect  against  chemical  corrosion  from  the  soil.  In  France,  gas 
engineers  stated  that  insulating  coverings  were  being  studied,  but 
it  was  not  believed  that  they  would  prove  practicable. 

In  England  insulating  coverings  are  not  considered  good  pro- 
tection against  stray  railway  currents.  High  pressure  gas  pipes 
have  been  covered  with  pitch  canvas,  and  the  London  Water 
Board  pipes  are  provided  with  an  asphalt  dip  coating  but  more 
as  a  protection  against  chemical  corrosion. 

17.  Electric  Cables. 

Cables  are  more  frequently  laid  solid  in  the  ground,  and  con- 
duits are  used  less  than  in  America.  Metal  conduits  are  only 
occasionally  used  in  England;  where  they  are  used  the  cable 
sheaths  are  bonded  to  the  conduits.  Insulating  joints  are  not 
used  in  Germany  or  England  for  telephone  cables. 

D.     ELECTROLYSIS  CONDITIONS 
1.  General. 

Among  the  countries  visited  it  was  found  that  in  Germany 
engineers  and  managers  of  the  utilities  concerned  were  fully  alive 
to  the  problem  of  stray  current  electrolysis,  and  they  were  well 
informed,  due  largely  to  the  work  of  their  Earth  Current  Com- 
mission. In  England,  although  engineers  and  managers  were 
generally  informed,  there  was  little  lively  interest  in  the  question, 
due  probably  to  the  fact  that  there  does  not  exist  any  acute 
electrolysis  problem. 

In  France,  the  Government  and  the  Paris  municipality  had 
recently  (1914)  appointed  a  Commission  to  investigate  the  subject 
of  stray  current  electrolysis  and  make  recommendations  regarding 


152  EUROPEAN  PRACTICE 

the  situation  in  the  City  of  Paris.  In  Italy,  troubles  from  electrol- 
ysis have  been  considered  insignificant.  Some  of  the  larger  sys- 
tems in  important  cities  are  alive  to  the  situation  and  are  follow- 
ing with  interest  the  developments  in  other  countries. 

Favorable  reports  of  immunity  from  electrolysis  troubles  were 
based,  as  in  Italy,  on  the  absence  of  complaints.  It  was  note- 
worthy that  reports  of  damage  were  greatest  where  most  thorough 
investigation  had  been  made. 

2.  Voltage  and  Current  Conditions ;  Experience  with  Electrolysis. 

(a)  Germany.  Considerable  damage  was  found  in  many  cities 
prior  to  the  application  of  the  Earth  Current  Regulations ;  in  one 
case  service  pipe  trouble  occurred  as  often  as  once  a  month. 
Generally  however,  extensive  damage  was  not  known  until  it  was 
revealed  by  investigation.  Thus,  many  of  the  cities  which  were 
surveyed  by  the  Commission,  and  where  more  or  less  corrosion 
was  found,  had  previously  reported  no  damage.  In  the  past 
the  majority  of  troubles  have  been  on  gas  and  water  pipes,  or  at 
least  these  have  received  more  attention  in  the  reports.  No  cases 
of  extensive  damage  to  cable  sheaths  were  found. 

Many  very  thorough  tests  have  been  made  in  Germany  and  a 
large  majority  of  these  have  shown  that  corrosion  was  being  pro- 
duced by  stray  railway  currents.  In  general,  the  pipe  owning 
interests  stated  that  the  situation  was  such  that  the  work  of  the 
Earth  Current  Commission  was  urgently  needed.  Gas  and  water 
experts  expressed  the  opinion  that  the  regulations  were  too  lenient, 
while  the  railway  experts  felt  that  they  were  too  severe,  main- 
taining that  a  considerable  amount  of  corrosion  ascribed  to  stray 
railway  current,  was  in  fact,  due  to  other  sources,  or  to  self- 
corrosion. 

In  general,  present  conditions  in  Germany  were  considered 
satisfactory  where  the  electric  railways  have  conformed  to  the 
Commission  Regulations ;  or  where  conditions  were  already  equally 
good.  In  other  cases  the  conditions  were  considered  to  be  un- 
satisfactory. The  more  prosperous  companies  and  municipalities 
spent  money  for  improvements  after  the  publication  of  the  Regula- 
tions of  the  Earth  Current  Commission.  Exact  information  was 
not  available  regarding  the  number  of  places  where  changes  had 
been  made,  but  the  best  information  indicated  that  the  number 
was  between  20  and  30.  Of  these,  Danzig,  Strasburg  and  Erfurt 
expended  about  100,000  Marks  each,  rearranging  the  resistances 
of  exivSting  return  conductors,  and  Dresden  was  engaged  in  1914 


EUROPEAN  PRACTICE  153 

in  insulating  the  existing  bare  return  conductors.  Generally, 
the  most  important  cities  were  rapidly  improving  their  return 
circuit  conditions.  Also,  other  undertakings  not  subject  to  the 
Regulations  were  changing  over  voluntarily  for  reasons  of  policy 
or  economy,  or  as  the  result  of  compromise  to  avoid  litigation; 
this  was  said  to  be  the  case  in  30  or  40  important  towns.  A 
litigated  case,  in  Mansfeld,  was  decided  against  the  gas  company 
on  legal  grounds  as  the  railway  existed  before  the  gas  plant. 

Where  return  circuits  have  not  been  remodeled  in  accordance 
with  the  Commission  Regulations,  overall  voltage  limits  vary 
greatly,  but  in  the  majority  of  cases  they  are  between  5  and  10 
volts  overall.  Measurements  were  made  by  the  Sub-Committee 
of  one  large  installation  having  negative  feeders  equal  in  number 
and  area  to  the  positive  feeders;  it  was  found  that  the  maximum 
drops  in  rails  were  well  within  the  limits  prescribed  by  the  Regu- 
lations. 

(b)  Italy.     From  a  survey  made  about  1908  in  a  city  of  Italy, 
it  was  found  that  the  maximum  difference  of  potential  in  the  rails 
between  the  station  and  points  about  three  miles  (5  kilometers) 
distant  were  as  great  as  17.5  volts.     In  this  installation  they  had 
not  received  complaints  of  serious  damage  by  electrolysis,  except 
a  few  gas  service  pipes,  although  the  railroad  itself  had  experienced 
some  difficulties  on  water  pipes  at* one  of  its  yards. 

(c)  France.     The    Sub-Committee's    investigation    was    some- 
what limited  in  France.     No  adequate  or  complete  tests  have 
been  made,  although  some  testing  has  been  done  in  Paris  follow- 
ing the  development  of  trouble.     It  is  stated  that  tramways  in 
France  generally  endeavor  to' observe  the  1  volt  per  km.  limit 
(1.6  volts  per  mile),  and  that  potential  differences  between  pipes 
and  rails  rarely  exceed  one  volt. 

In  general  serious  electrolysis  troubles  were  found  only  in  a 
few  places,  either  created  by  heavy  traffic  lines  or  by  peculiar 
conditions,  not  readily  explainable.  Outside  of  Paris  there  is 
little  damage  caused  by  tramway  systems.  In  the  suburbs  of 
Paris  all  underground  pipe  systems  are  more  or  less  affected. 
In  Paris  60  to  70  cases  of  damage  to  pipes  have  been  found  in  a 
year — the  actual  cost  of  repairs  was  estimated  to  be  60,000  francs, 
but  it  was  held  that  the  paramount  consideration  was  the  danger 
to  security  of  service,  since  nearly  all  cases  caused  property  losses 
in  buildings,  although-  there  were  no  explosions. 

At  least  a  third  of  the  total  number  of  cases  reported  were  due 
to  the  rearrangement  of  the  old  two- wire,  three-wire  and  five- 


154  EUROPEAN  PRACTICE 

wire  systems  of  electric  light  distribution,  but  these  troubles 
were  of  a  temporary  character  and  were  promptly  remedied  as 
soon  as  discovered.  In  the  other  cases,  due  to  stray  railway 
currents,  the  troubles  were  persistent.  About  twenty  litigated 
cases  for  electrolysis  damage  were  pending  in  Paris  in  1914. 

A  very  considerable  amount  of  damage  in  Paris  is  due  to  the 
"Metropolitan"  subway  system  which  claims  exemption  from  the 
1  volt  per  km.  (1.6  volts  per  mile)  regulation,  not  being  a  tram- 
way. At  one  place  in  Paris  a  potential  difference  of  6  volts  be- 
tween a  railway  structure  and  a  pipe  was  observed  by  the  Sub- 
Committee. 

There  are  few  telephone  cable  troubles  in  Paris  due  to 
electrolysis. 

(d)  Great  Britain.  Considerable  damage  is  said  to  have 
occurred  in  the  early  days  of  electric  traction  in  England,  although 
such  damage  was  apparently  insignificant  compared  to  conditions 
familiar  in  America  during  the  same  period.  Practically  no 
damage  has  occurred  in  recent  years,  and  certainly  no  extensive 
damage.  Two  or  three  cases,  local  in  character  and  of  small 
extent,  have  occurred  in  localities  where  the  Board  of  Trade 
Regulations  were  complied  with. 

In  England  there  is  very  little  good  evidence  in  the  way  of  tests, 
and  the  general  statements  of  Immunity  are  based  on  absence  of 
trouble.  The  Post  Office,  and  the  South  Metropolitan  Gas 
Company  of  London,  both  make  systematic  tests  and  find  no 
trouble  except  that  the  Post  Office  has,  from  time  to  time,  en- 
countered difficulties  quite  local  in  character,  due  to  stray  currents. 
.The  Board  of  Trade  Regulations  are  not  considered  onerous  by 
any  of  the  railway  engineers  consulted.  All  authorities  represent- 
ing the  pipe  owning  companies,  the  tramways,  the  state  telegraph 
and  telephone,  and  the  Board  of  Trade,  were  unanimous  in  stating 
that  the  electrolysis  situation  for  the  properties  under  their  re- 
spective control  was  entirely  satisfactory.  Nevertheless,  there  is 
considerable  feeling  -among  the  privately  owned  gas  companies 
that  they  are  not  adequately  protected,  since,  as  noted  elsewhere, 
they  cannot  recover  damages  in  case  corrosion  occurs  where 
Regulations  are  complied  with. 

Overall  rail  drops  for  tramways  in  England  are  generally  very 
much  lower  than  the  Board  of  Trade  requirement,  averaging 
probably  2.5  to  3  volts,  with  the  exception  of  occasional  drops, 
which  may  be  as  high  as  15  or  20  volts,  due  to  extraordinary 
traffic  at  football  matches,  etc.  The  average  overall  drops  for 


EUROPEAN  PRACTICE  155 

several  large  cities  visited  by  the  Sub-Committee  during  June  and 
July,  1914,  were  about  2  volts.  Glasgow,  which  voluntarily 
adopted  a  2  volt  rail  drop,  Manchester,  and  other  large  towns, 
have  extraordinarily  low  rail  drops. 

The  electrification  of  branch  railway  lines  has  been  carried  out 
to  a  considerable  extent  since  1914,  and  some  data  were  obtained 
in  1920  concerning  the  voltage  drop  in  the  return  circuits  of  such 
lines.  Two  electrified  sections  of  an  extensive  railway  system 
are  reported  to  have  maximum  instantaneous  voltage  drops  as 
follows : 

A 43  volts 

B 77  volts 

Another  railway  reports  in  general  that  the  voltage  drop  for  its 
electrified  sections  is  higher  than  that  permitted  for  tramways; 
and  in  particular  that  the  worst  section  gives  a  maximum  drop 
of  25  volts  for  15  to  20  seconds,  with  instantaneous  maxima 
considerably  higher. 

Potential  differences  between  pipes  and  tramway  rails  are  said 
to  be  generally  less  than  1  volt. 

E.     MISCELLANEOUS  OBSERVATIONS 

1.  Drainage  System. 

Electrical  drainage  as  a  palliative  measure  for  electrolysis 
was  formerly  applied  in  one  or  two  cases  in  Germany,  notably  in 
Aachen,  but  it  was  abandoned  on  account  of  damage  produced 
by  it,  first  due  to  joint  corrosion,  and  second,  damage  to  other 
underground  structures.  It  is  condemned  by  the  engineers  of  the 
Earth  Current  Commission. 

In  England,  drainage  is  not  approved  as  a  general  measure 
to  afford  relief  from  stray  current,  although  there  are  a  few  specia 
instances  of  its  application  to  the  tramway  company's  own  lead 
covered  cables,  where  the  common  practice  is  to  bond  to  the  rails 
at  many  points. 

2.  Corrosive  Effects  of  Soil;  Earth  Resistance. 

In  Germany  the  possibility  of  chemical  corrosion  (that  is, 
corrosion  without  an  external  supply  of  electricity)  is  recognized, 
and  distinction  is  made  between  such  corrosion  and  that  pro- 
duced by  stray  currents.  Pipe  corrosion  has  actually  been  found 
under  conditions  where  it  could  not  have  been  produced  by  stray 
currents.  No  definite  information  was  obtained  in  England 


156  EUROPEAN  PRACTICE 

regarding  the  corrosive  properties  of  soil,  but  it  was  stated  that 
chemical  corrosion  was  known  to  occur.  Such  corrosion  does  not, 
however,  produce  acute  conditions  as  in  electrolysis;  it  is  rviore 
like  ordinary  oxidation. 

German  reports  gave  the  resistance  of  soil  as  varying  from  1 
ohm  to  2,000  ohms  per  cubic  meter  (1.3  ohms  to  2,616  ohms  per 
cubic  yard),  averaging  about  100  ohms  per  cubic  meter,  (131  ohms 
per  cubic  yard) .  In  England  no  specific  information  was  obtained 
concerning  earth  resistance.  One  report  states  that  the  provi- 
sions of  clause  5A  of  Tramway  Regulations  (for  two  earth  plates 
not  less  than  20  yards,  (18  meters)  apart  between  which  an  E.M.F. 
not  more  than  4  volts  shall  produce  current  of  2  amperes)  cannot 
be  met  even  at  permanent  water  level,  and  that  in  general  the 
apparent  resistance  is  about  twice  that  required  by  Regulations. 

3.  Electrolysis  Testing  Methods. 

In  England  very  little  testing  is  done  to  investigate  electrolysis 
questions  and  no  technique  has  been  developed  for  such  work. 
The  only  extensive  work  in  recent  years  is  that  of  the  Cunliffe 
brothers,  and  their  work  was  directed  mainly  toward  the  investiga- 
tion of  certain  theoretical  questions  rather  than  toward  the 
systematic  investigation  of  actual  experience  with  stray  currents. 

In  .Germany  the  work  of  the  Earth  Current  Commission  has 
been  already  noted.  The  surveys  made  by  the  engineers  of  the 
Commission  are  systematically  planned;  they  are  made  in  the 
most  excellent  technical  manner.  The  reports  are  quite  uniform 
in  character;  they  start  with  a  general  investigation  of  geological 
conditions,  the  character  of  the  soil,  ground  water,  etc.,  continuing 
with  a  general  survey  of  the  present  condition  of  the  railway 
property,  including  distribution  of  load,  track  and  rail  resistance, 
location  and  loading  of  supply  and  return  circuit  cables  and  any 
other  electrical  data  relating  to  the  investigation.  The  surveys 
then  take  up  the  specific  measurements  relating  to  stray  current, 
such  as  potential  differences  between  pipes  and  rails,  current  in 
pipes,  and  so  forth.  Reasoning  from  the  data  presented,  recom- 
mendations are  made  for  improving  conditions,  where  improve- 
ments are  needed,  sometimes  with  estimates  for  the  cost  of  the 
work.  In  some  cases  a  supplementary  report  is  made  which  shows 
the  conditions  after  the  changes  have  been  made.  The  conclusions 
arrived  at  appeared  to  be  practicable  and  reasonably  acceptable 
to  all  parties  concerned. 


EUROPEAN  PRACTICE  157 

4.  Economic  Aspects  of  the  Electrolysis  Problem. 

About  forty  per  cent  of  the  electric  railway  systems  in  Germany, 
and  about  seventy  per  cent  in  Great  Britain,  are  municipally 
owned.  In  Germany  one  authority  thought  that  municipalities 
were  more  ready  than  private  companies  to  spend  money  for  the 
purpose  of  improving  their  return  circuits,  but  in  England  it  was 
thought  that  there  was  no  difference  in  this  respect.  It  was  said 
in  Germany  that  where  municipalities  owned  the  water,  gas,  and 
tramway  systems,  they  may  prefer  to  assume  the  cost  of  damage 
rather  than  make  large  expenditure  for  protecting  their  pipes. 

Also  in  Germany,  a  study  of  the  survey  reports  of  the  Earth 
Current  Commission  indicated  that  in  no  case  was  the  yearly  cost 
of  repairs  for  damage  by  electrolysis  of  such  amount  that,  on  the 
surface,  large  expenditures  for  improvements  would  be  justified. 
The  Commission,  however,  while  recognizing  the  importance  of 
the  financial  aspect  of  the  problem,  still  recommended  the  adop- 
tion of  the  relatively  expensive  remedies  for  the  reason  they  state — 
"that  the  repairs  will  certainly  become  more  frequent  with  lapse 
of  time,  and  besides  the  increased  expense  so  caused,  there  is  the 
liability  of  service  interruption,  disturbance  of  traffic,  pavement 
replacement  and  even  danger  of  explosion  to  be  considered." 

Opinions  differed  in  Germany  as  to  whether  or  not  the  prevailing 
regulations  constituted  a  financial  hardship.  In  England,  the 
Board  of  Trade  Regulations  are  nowhere  considered  a  hardship, 
and  where  inquiry  was  made  as  to  whether  the  existing  regulations 
had  retarded  the  development  of  electric  railways,  the  authorities 
consulted  uniformly  stated  that  this  was  not  the  case.  It  appears 
that  in  fact  a  saturation  point  has  been  reached,  and  busses  are 
being  used  where  tramways  would  not  pay.  Traffic  conditions 
are  said  to  be  quite  as  heavy  in  England  as  in  the  United  States. 
Only  one  authority  in  England  ventured  an  estimate  of  the  aver- 
age load  factor  for  English  electric  railways  systems;  he  estimated 
it  to  be  thirty-five  per  cent. 

5.  Application  to  American  Conditions. 

Disputes  on  account  of  electrolysis  troubles  have  been  prevalent 
in  the  past  in  all  countries  having  any  considerable  electric  railway 
development,  before  systematic  cooperative  studies  or  regulations 
were  applied;  this  in  spite  of  the  fact  that  the  mode  of  life  and 
distribution  of  population  and  industries  are  more  favorable  than 
in  American  cities.  The  average  weight  of  cars  in  foreign  cities 
is  less  than  in  America,  and  the  tramway  traffic  and  power  re- 


158  EUROPEAN  PRACTICE 

quirements  may  be  one-fifth  or  less  in  Europe  than  in  America 
for  cities  of  the  same  population. 

A  city  like  Berlin  with  over  2,000,000  inhabitants  handled  all 
of  its  transportation  with  a  maximum  load  of  about  30,000  kw. 
(Chicago  with  over  2,200,000  population  required  a  maximum  load 
of  about  200,000  kw.)  Manchester  with  a  population  of  1,250,000 
and  Glasgow  with  1,000,000  had  traction  loads  of  11,000  kw.  and 
11,500  kw.  respectively.  (Boston  and  the  territory  served  by  its 
traction  system  with  about  1,150,000  people,  required  station 
capacity  of  75,000  kw.)  Milan  with  a  population  of  over  600,000 
had  a  traction  load  of  approximately  8,000  kw.,  and  Nurnberg 
with  350,000  inhabitants  used  only  1,000  kw.  (The  city  of 
Worcester,  Mass.,  with  a  population  of  approximately  160,000 
required  power  station  capacity  of  7500  kw.).  These  comparisons 
should  be  taken  into  consideration  in  applying  to  this  country  the 
results  of  this  investigation  of  foreign  practice. 

These  comparisons,  however,  should  not  be  taken  as  a  definite 
index  to  comparative  electrolysis  conditions,  since  many  other 
factors  are  involved.  Regardless  of  the  degree  of  improvement 
which  economical  limitations  may  make  permissible  to  accomplish 
in  local  situations,  the  fundamentals  for  the  solution  of  the  elec- 
trolysis problem  evolved  abroad  merit  the  most  careful  study  to 
ascertain  their  possible  application  to  American  conditions. 

F.     SUMMARY 

In  Europe,  the  effectiveness  of  the  cooperative  or  regulatory 
measures  applied  to  the  electrolysis  problem  may  be  summarized 
as  follows : 

Germany,  through  voluntary  cooperation,  has  probably  remedied 
the  former  dangerous  electrolysis  conditions  for  all  of  its  important 
systems.  The  instrumentality  of  agreements  on  definite  technical 
standards  was  sought  in  preference  to  legislation. 

France  has  not  been  as  successful  in  bringing  prompt  results 
through  legislation  as  has  Germany  through  technical  cooperation. 

England  which  has  had  government  regulation  for  many  years 
has  now  no  electrolysis  troubles  or  disputes. 

Italy  will  probably  give  more  consideration  to  the  subject  of 
electrolysis  whenever  the  general  conditions  will  permit. 

The  methods  followed  to  attain  the  satisfactory  results  obtained 
abroad  are  these : 

1.  Maintenance  of  good  bonding. 


EUROPEAN  PRACTICE  159 

2.  Elimination  of  intentional  contacts,  and  liberal  separa- 
tion wherever  possible,  of  pipes  and  rails. 

3.  Avoidance  of  bare  copper  returns  and  use  of  insulated 
returns  in  all  installations  where  the  conductivity  of  the  rail 
alone  would  give  a  too  great  maximum  drop. 

4.  Use  of  insulated  return  feeders  with  balancing  resist- 
ances, or  to  a  lesser  extent  ''boosters"  for  the  purpose  of 
maintaining  equality  of  rail  potential  at  the  feeding  points 
of  all  reeders. 

Small  feeder  drops  and  frequent  substations  to  give  close 
line  regulation. 

G.     EUROPEAN  REGULATIONS  ADOPTED  AND  PROPOSED 

GERMANY— EARTH  CURRENT  COMMISSION'S  RECOMMENDATIONS 

RECOMMENDATIONS    OF    THE   GERMAN    EARTH    CURRENT   COMMISSION    AS 
ADOPTED  BY  THE  GAS,  WATER,  AND  RAILWAY  INTERESTS  OF  GERMANY. 

Regulations  for  the  protection  of  gas  and  water  mains  from 
the  electrolytic  action  of  currents  from  direct  current  electric 
railways  which  use  the  rails  as  a  return. 

Accepted  for  two  years  at  the  yearly  meeting  of  1910  and 
for  a  further  two  years  at  the  yearly  meeting  of  1912. 

Published  in  the  Electrotechnische  Zeitschrift,  1910,  page 
491,  and  1911,  page  511. 

Section  1.     Application  of  Rules. 

The  following  rules  govern  the  installation  of  direct  current 
railways  or  sections  of  direct  current  railways  which  use  the  rails 
for  carrying  the  return  current.  Unless  otherwise  mentioned  the 
herein  given  admissible  potential  values  should  be  adhered  to 
when  laying  out  new  railways.  For  determining  the  resistance 
of  a  line,  the  rails  only  must  be  taken  into  account  as  current 
carrying  mediums  and  the  assumed  resistance  of  the  rails,  as  well 
as  the  assumed  percentage  increase  of  resistance  due  to  the  bonding 
must  be  stated. 

These  values  must  not  be  exceeded,  either  when  making  the 
necessary  calculations  or  by  the  plant  when  in  actual  normal 
operation. 

These  rules  do  not  apply  when  railways  are  laid  with  special 
track  or  when  the  rails  are  laid  on  wooden  sleepers,  in  which  case 
there  is  generally  an  air  clearance  between  the  rails  and  the  stone 
ballast;  but  the  rules  do  apply  if  this  air  clearance  does  not  exist, 
as  at  grade  crossings,  unless  an  equivalent  insulation  is  provided 


160  EUROPEAN  PRACTICE 

for  locally.  Further,  these  rules  do  not  apply  to  railway  lines 
which  do  not  approach  closer  than  200  meters  to  an  underground 
pipe  network. 

Explanation* 

The  regulations  apply  only  to  direct  current  railroads  or  sec- 
tions of  such,  using  the  rails  as  conductors.  Railroads  not  using 
the  rails  as  conductors  are  eliminated  from  the  start,  because  the 
same  do  not  send  any  currents  into  the  earth  and  therefore  cannot 
have  any  damaging  influence  on  the  pipes.  According  to  the 
experience  reached  so  far,  alternating  current  seems  to  have  very 
little  effect,  so  that  any  extension  of  these  rules  to  cover  also 
alternating  current  railways  does  not  seem  justified.  At  any 
rate,  the  conditions  produced  by  alternating  current  railways  are 
not  yet  sufficiently  understood  to  allow  of  establishing  any  restric- 
tions in  regard  to  their  equipment  and  operation  for  the  protection 
of  pipes. 

In  case  a  railroad  is  operated  partly  with  direct  current  and 
partly  with  alternating  current,  these  regulations  apply  only  to 
those  sections,  the  rails  of  which  carry  direct  current.  The  fixed 
upper  limits  of  permissible  potentials  apply  to  the  design  of  the 
plant,  unless  otherwise  stated,  and  in  the  calculations  only  the 
rails  and  the  bonds  are  to  be  considered  as  far  as  the  conductivity 
and  the  resistances  of  the  conductors  are  concerned.  The  assumed 
resistance  of  the  rails  and  the  increase  of  same  by  the  resistance 
of  the  bonds  is  to  be  stated,  and  such  limiting  values  are  not  to  be 
exceeded  either  by  calculations  or  in  practice. 

The  earth  as  a  shunt  is  not  considered.  Through  contact  of 
the  rail  network  with  the  ground,  a  part  of  the  current  passes 
into  the  ground  and  the  potentials  of  the  rail  network  are  thereby 
lowered  as  compared  with  a  case  of  perfect  insulation  from  the 
ground,  the  effect  becoming  greater,  the  more  the  current  passes 
into  the  ground.  It  is,  therefore,  not  correct  to  take  the  differ- 
ences of  potentials '  as  found  immediately  after  the  construction 
of  a  rail  network  as  a  basis  for  estimating  the  safety  against 
damaging  influences,  but  it  is  necessary  to  go  back  to  the  first 
cause,  that  is  to  say,  the  differences  of  potential  as  they  would  be 
if  the  rails  were  completely  insulated. 

This  rule  allows  of  an  exact  calculation  of  the  conditions  during 


*NOTE:     This   explanation   and   the  other   following  are  included  in  the 
German  Earth  Current  Commission's  recommendations. 


EUROPEAN  PRACTICE  161 

the  design  of  the  plant  without  any  uncertain  and  varying  values 
for  different  localities.  The  limit  values  are  not  to  be  exceeded 
either  during  the  calculations  or  at  the  actual  practical  test. 
The  method  of  the  practical  test  will  be  discussed  in  Section  3. 
The  projection  of  the  plant  is,  therefore,  to  be  based  on  assump- 
tions as  correct  as  possible  with  regard  to  the  resistance  of  the 
rail,  the  cables,  and  the  consumption  of  current,  and  it  is  advis- 
able to  consider  also  a  later  increase  of  the  traffic. 

Railroads,  the  rails  of  which  are  insulated  on  special  roadbeds, 
generally  have  such  a  great  resistance  against  the  earth  that 
passage  of  current  into  the  ground  of  such  magnitude  as  to  be  con- 
sidered dangerous  to  pipes  does  not  occur.  Higher  potentials, 
therefore,  are  permissible  for  such  railroads,  assuming  that  a 
sufficient  insulation  is  provided  for  also  on  grade  crossing,  etc. 

As  a  means  to  this  end  are  to  be  considered : 

Insulating  strata  between  rails  and  ground,  for  instance,  tar 
paper,  which  must  extend  on.  all  sides  sufficiently  beyond  the 
place  in  question;  or  the  surrounding  of  the  pipes  with  insulating 
material.  Such  places  are  to  be  inspected  from  time  to  time  to 
ascertain  the  effect  of  such  insulation. 

For  the  exemption  from  these  regulations  the  laying  of  the  rails 
on  a  special  roadbed  is  required,  because  it  is  only  in  this  way  that 
a  permanent  insulation  can  be  reached  and  maintained.  About 
the  details  of  the  system  of  insulation  to  be  used,  no  rules  were 
issued.  A  lasting  insulation  is  to  be  guaranteed  by  the  way  in 
which  the  rails  are  laid.  The  laying  of  rails  on  wooden  ties  as 
mentioned  above  is  intended  as  an  example  only.  At  any  rate  to 
secure  satisfactory  insulation  it  is  imperative  that  the  rails  be 
nowhere  in  contact  with  the  moisture  of  the  ground,  as  this 
greatly  favors  the  passage  of  the  current  into  the  ground. 

Tracks  which  are  at  all  points  at  least  200  m.  distant  from  any 
pipes  are  exempt,  because  any  current  coming  over  such  an 
extended  area  spreads  to  such  a  degree  that  its  density  cannot 
possibly  be  harmful.  In  this  respect  concession  has  been  made 
to  long  outlying  railway  lines  because  the  subjection  of  such  to 
these  regulations  would  entail  great  economic  disadvantages  in 
certain  cases.  The  maintenance  of  good  conductivity  on  such 
outlying  sections  is  to  be  strongly  recommended  so  as  to  prevent 
the  return  currents  from  reaching  a  dangerous  density  where 
such  sections  join  the  rails  of  an  inner  rail  network,  i.e.,  a  density 
exceeding  the  limit  given  in  Section  5. 


162  EUROPEAN  PRACTICE 

Section  2.    Rail  Conductors 

All  rails  serving  as  return  conductors  should  be  built  with  regard 
to  this  requirement,  should  be  made  as  good  conductors  as  possible, 
and  should  always  be  kept  in  good  order. 

The  percentage  of  increase  of  the  resistance  of  a  given  length 
of  track  due  to  the  bonding  should  not  exceed  the  value  assumed 
when  laying  out  the  railway,  and  must  not  be  more  than  20% 
more  than  the  resistance  of  the  same  length  of  track  if  the  rails 
were  without  joints  and  of  the  same  cross-section  and  the  same 
specific  conductivity.  On  laying  out  a  railway  line  consisting  of 
main  and  auxiliary  rails,  the  combined  cross-section  of  both  rails 
can  only  be  taken  into  account  when  determining  the  resistance 
of  the  track,  provided  the  auxiliary  as  well  as  the  main  rails  are 
properly  bonded  and  cross  bonded. 

At  rail  crossings  and  at  switches,  the  rails  must  be  well  bonded 
by  special  bridge  bonds. 

On  single  tracks  as  well  as  on  lines  where  several  tracks  are 
lying  side  by  side  the  rails  must  be  efficiently  cross  bonded  and 
these  cross-  and  bridge-bonds  must  have  a  conductivity  at  least 
equal  to  a  copper  conductor  of  80  square  millimeters. 

At  all  movable  bridges  or  similar  structures  which  necessitate 
an  interruption  of  the  rails,  special  insulated  conductors  have  to 
be  provided  which  secure  a  continuous  connection  between  the  two 
rail  ends.  In  such  cases,  the  voltage  drop  at  average  load  must 
not  exceed  5  millivolts  for  each  meter  distance  between  the  inter- 
rupted rails. 

All  current  carrying  conductors  which  are  connected  to  the 
rails,  must  be  insulated  from  earth,  excepting  short  connections 
such  as  bonds,  cross-bonds  and  bridge-bonds  at  switches  and 
turntables.  If  such  bonds  are  laid  not  deeper  than  25  centimeters 
into  the  earth,  they  may  be  bare  conductors. 

Explanation 

The  first  condition  for  the  reduction  of  stray  currents  and  for 
the  effectiveness  of  all  the  proposed  precautionary  measures,  is 
the  good  conductivity  of  the  tracks  and  the  maintenance  of  this 
conductivity.  High  resistances  of  the  single  sections  cause  an 
increase  of  the  current  passing  into  the  ground.  The  maintenance 
of  the  good  conductivity  of  the  rails  also  is  to  the  economic  interest 
of  the  railroad,  because  a  bad  conductivity  will,  under  certain 
circumstances,  cause  loss  of  energy. 

It  is  not  desirable  to  issue  rules  concerning  the  cross-sections 


EUROPEAN  PRACTICE  163 

of  rails  or  for  the  conductivity  of  the  steel  because  the  cross-sec- 
tion and  the  chemical  composition  of  the  steel  are  both  determined 
by  mechanical  considerations;  the  conductivity  is  dependent  on 
the  composition  of  the  steel,  while  the  conductance  of  the  rail 
depends  on  both  the  conductivity  and  the  profile. 

The  resistance  of  a  rail  network  is  widely  influenced  by  the 
quality  of  the  electrical  connections  of  the  rails  at  their  joints. 

The  rules  do  not  recommend  one  or  another  system  of  connec- 
tions at  the  joints,  but  give  data  covering  the  permissible  increase 
of  the  resistance  by  such  connections. 

In  consideration  of  the  varying  resistance  of  rails  of  different 
profile,  it  is  not  possible  to  establish  a  uniform  permissible  resist- 
ance for  a  bond  but  the  permissible  increase  of  the  total  resistance 
of  a  section  by  all  the  bonds  is  given.  This  increase  must  not  be 
over  20  per  cent.  Inside  of  these  limits  the  designing  engineer 
may  assume  any  increase  of  the  resistance  by  the  bond,  but  it 
must  be  considered  that  the  increase  assumed  must  be  perma- 
nently maintained  later  on  (compare  Sections  6  and  3) . 

It  will  be  well  to  assume  during  the  design  of  the  plant,  the  in- 
crease of  resistance  of  the  bonds  as  very  near  the  permissible  limit. 
This  is  very  important  when  shorter  rails  are  to  be  used,  with  the 
consequent  greater  number  of  joints,  the  maintenance  of  which  is 
correspondingly  more  difficult  and,  therefore,  an  increase  of 
resistance  through  deficient  bonds  to  be  expected.  The  conduc- 
tivity of  rails  is  to  be  ascertained  on  a  number  of  samples  before 
the  rails  are  laid,  so  as  to  have  a  guarantee  that  the  calculated 
resistance  will  correspond  to  the  resistance  of  the  finished  work. 

The  measurement  of  the  resistance  is  made,  by  measuring  the 
current  and  the  potential  on  a  raitas  long  as  possible  and  insulated 
from  its  supports ;  the  potential  terminals  should  include  a  part  of 
the  circuit  between  the  current  contacts  and  they  should  be  at 
least  0.5  meter  distant  from  these  current  contacts.  A  simple 
calculation  gives  the  conductivity  of  the  rail  by  using  the  value 
shown  by  ammeter  and  voltmeter.  The  conductivity  of  the  rails 
now  in  use  is  generally  found  to  be  between  4  and  5.5  Siemens 
(10.5  to  14.4  times  the  resistivity  of  copper). 

In  cases  where  main  and  auxiliary  rails  are  to  be  used  and  where 
the  combined  cross-section  of  both  is  taken  into  calculation,  the 
conductivity  of  the  auxiliary  rail  also  is  to  be  measured  as  the 
same  may  differ  considerably  from  the  conductivity  of  the  main 
rail. 

At  crossings  and  switches  a  loosening  of  the  rail  connections 


164  EUROPEAN  PRACTICE 

will  take  place  caused  by  the  vibrations  brought  about  by  the 
passage  of  the  rolling  stock,  for  which  reason  such  places  are  to  be 
bridged  specially  by  electrical  conductors.  The  cross  connections 
serve  the  purpose  of  eliminating  differences  of  potentials  between 
tracks  running  side  by  side  and  also  to  insure  a  good  metallic 
connection  between  the  rails  on  one  side  of  a  track  in  the  case  of  a 
temporary  low  conductivity  of  single  joints  or  interruptions. 

It  seems  advisable  in  consideration  of  the  different  length  of 
rails,  not  to  give  an  absolute  distance  between  the  cross  connec- 
tions, but  to  establish  their  number  by  the  number  of  joints. 
The  bonds  and  cross-connections  may  be  of  any  material  as  long 
as  their  conductivity  reaches  at  least  that  of  a  copper  connector 
of  80  square  mm.  For  the  connection  of  interrupted  tracks,  as 
for  instance  at  movable  bridges,  insulated  cables  are  required 
because  of  the  presence  of  water  or  other  substances  in  the  soil, 
which  highly  favor  the  passage  of  currents  into  the  ground.  The 
highest  permissible  drop  in  potential  at  average  load  has  been 
fixed  at  5  millivolts  per  meter  distance  between  the  places  of 
interruption,  to  insure  a  small  difference  of  potential  between 
these  points. 

Furthermore  care  is  to  be  taken  that  the  tracks  in  a  movable 
bridge  are  in  good  contact  with  the  tracks  on  both  sides  of  it. 
The  following  is  an  example  of  the  calculation  of  a  cable  bridging 
across  the  gap. 

When  the  distance  between  the  tracks  at  the  point  of  interrup- 
tion equals  30  meters,  the  permissible  difference  of  potential, 
therefore,  is  5  x  30  which  equals  150  millivolts.  The  current  to 
be  carried  across  is  assumed  to  be  120  amperes  and  the  length  of 
cable  30  meters.  Assuming  a  specific  resistance  of  17.5  milliohms 
per  meter  and  square  millimeter,  the  resulting  cross-section  is: 

17.SXL/      17.5X30X120 

q  —  -  —=-      —  —  =  420  sq.  mm. 

€  1  O\J 

Inasmuch  as  the  increase  of  the  surface  contact  between  the 
conductors  and  ground  results  in  an  increase  of  the  current  pass- 
ing from  the  conductors  into  the  ground,  the  conductors  connected 
to  the  rails,  especially  those  lying  deep  enough  to  come  into 
contact  with  the  moisture  of  the  ground,  are  to  be  insulated 
conductors.  Only  short  connections,  such  as  jumpers  on  cross- 
ings and  switches,  are  exempt  from  this  rule  on  account  of  the  same 
not  lying  deeper  than  25  cm.  under  the  surface,  which  means  that 
they  hardly  come  into  contact  with  the  moisture  of  the  ground. 


EUROPEAN  PRACTICE  165 

The  increase  of  surface  of  the  contacts  with  the  ground  by  these 
conductors  is  too  small  in  proportion  to  the  total  surface  of  the 
rail  network  to  cause  any  apprehension  regarding  the  currents 
passing  into  the  ground. 

Section  3.     Rail  Potential 

A  railway  network  is  divided  into  two  sections,  first,  the  open 
road  connecting  the  various  townships,  and  second,  the  urban 
network. 

In  the  urban  network  and  for  a  distance  of  2  km.  beyond,  the 
voltage  drop  between  any  two  rail  points  should  never  exceed 
2.5  volts  when  the  line  is  working  under  normal  conditions,  and 
the  drop  in  the  rails  for  each  kilometer  of  open  road  should  not 
exceed  1  volt.  Occasional  night  cars  are  not  to  be  considered  in 
determining  the  average  load. 

In  townships  through  which  only  a  single  line  is  run,  without 
local  rail  network,  the  total  voltage  drop  in  the  rails  must  not 
exceed  2.5  volts  from  end  to  end  of  the  township's  pipe  network. 

Any  apparatus  which  is  supplied  with  current  and  which  is 
connected  to  the  railway  network  must  not  increase  the  voltage 
drop  above  the  stated  limits. 

If  various  railway  systems  are  connected  together  either  through 
the  medium  of  the  rails  or  through  the  power  station,  each  system 
must  fulfill  the  above  conditions.  A  rail  system  in  a  township 
with  an  independent  pipe  network  has  to  comply  with  the  above 
regulations  also. 

Exceptions  from  these  rules  in  regard  to  the  voltage  drop  in  a 
railway  network  are  admissible  if  local  conditions  and  service 
necessitate  and  justify  such  exceptions.  If,  for  instance,  the 
service — as  is  the  .case  in  freight  yards — covers  only  a  small  por- 
tion of  the  day,  the  above  limits  of  rail  drops  may  be  exceeded. 
In  yards  with  a  service  up  to  three  hours  daily,  double  the  above 
values  are  permitted,  and  with  a  service  up  to  one  hour,  four  times 
the  above  values  are  allowed. 

Explanation 

As  mentioned  in  Section  1,  the  rail  network  is  to  be  considered 
as  insulated  from  the  ground,  so  that  the  earth  as  a  shunt  is  not 
considered. 

The  resistances  of  the  single  sections  are  to  be  calculated  from 
the  resistance  of  the  rails  under  observance  of  the  rules  in  Sections 
1  and  2. 


166  EUROPEAN  PRACTICE 

For  the  calculation  of  the  potentials  the  value  of  the  average 
current  is  to  be  used,  as  the  magnitude  of  electrolytic  decomposition 
of  the  pipe  metal  depends  on  the  quantity  of  current,  that  is  to 
say,  the  product  of  current  and  time.  The  highest  values  have 
not  to  be  considered  for  the  calculations.  To  find  the  consump- 
tion of  current  the  average  service  as  per  schedule  has  to  serve 
as  the  base. 

The  average  current  consumed  on  single  sections  can  be  cal- 
culated from  the  number  of  car  km.  or  ton  km.  to  be  covered,  by 
using  the  value  for  the  consumption  of  current  which,  according 
to  experience,  and  in  consideration  of  the  local  conditions,  is  used 
for  one  car  km.  or  ton  km. 

But  it  is  also  permissible  to  distribute  the  consumption  of 
current  over  the  whole  net  in  a  way  corresponding  to  the  locations 
of  the  single  trains  at  the  time  of  the  average  load  and  to  calculate 
for  each  train  the  consumption  of  current  taking  into  considera- 
tion the  weight  of  the  cars,  the  speed  and  operating  conditions 
(grade,  stops). 

In  regard  to  the  schedule,  the  difference  between  summer  and 
winter  service  is  to  be  considered.  The  increase  at  regular  inter- 
vals, as  for  instance  on  Sundays,  is  to  be  taken  into  account. 
Small  deviations  from  the  schedule,  as  for  instance,  single  night 
cars,  or  auxiliary  cars,  shall  not  be  considered,  because  the  first 
would  reduce  the  average  value  out  of  proportion,  and  the  fre- 
quency of  the  second  cannot  be  estimated  at  the  time  of  the  calcu- 
lations and  otherwise  are  not  of  any  appreciable  influence  on  the 
final  results. 

It  is  impossible  to  get  regulations  embracing  all  conditions 
and  possibilities  land  it  is  therefore  necessary  to  consider  all 
peculiarities  of  a  plant  during  its  projection..  If  there  are  any 
additional  places  connected  to  the  rails,  where  current  is  used  for 
stationary  motors,  station  lighting,  etc.,  these  are  to  be  considered. 

After  the  drops  in  potential  on  the  central  sections  have  been 
tabulated,  based  on  the  above  calculations,  the  distribution  of  the 
potential  in  the  rail  network  can  be  found.  In  addition  to  the 
foregoing  data  for  the  calculation  of  the  drop  in  potential  on  the 
single  sections,  consideration  is  to  be  given  to  the  proposed  return 
cables  and,  in  case  of  a  three  wire  system,  to  the  direction  of 
the  current  in  the  districts  of  different  polarity. 

Difference  in  potential  between  any  two  points  of  the  rail  net- 
work must  answer  the  following  conditions : 

Around  every  individual  pipe  network  (meaning  a  network  not 


EUROPEAN  PRACTICE  167 

in  metallic  contact  with  any  other  network)  and  also  around  single 
pipes,  a  zone  of  200  m.  is  to  be  circumscribed  and  all  tracks 
lying  outside  of  this  zone  are  not  be  to  considered  in  connection 
with  these  regulations,  as  per  last  part  of  Section  1 . 

For  each  of  the  rail  branches  lying  inside  of  these  individual 
pipe  networks,  the  following  rules  apply : 

If  there  are  any  branches  of  the  railroad  inside  of  a  pipe  net- 
work, including  the  200  m.  zones,  a  belt  2  km.  wide  is  to  be  laid 
around  the  inner  rail  network.  Inside  this  belt  the  potential  of 
the  rails  between  any  different  points  must  nowhere  exceed  2.5 
v.,  as  long  as  no  portion  of  the  rails  is  more  than  200  m.  distant 
from  the  nearest  pipe  along  its  total  length.  (Compare  Fig.  32). 

On  the  sections  outside  the  2.5  v.  districts,  the  drop  in  potential 
must  not  exceed  1  v.  per  km.  This  applies  to  outlying  sections 
which  are  shown  in  Fig.  32  by  heavy  dotted  lines. 

In  the  case  of  a  railroad  with  no  branches  (country  roads)  and  a 
pipe  network,  the  drop  in  potential  inside  the  pipe  network  must 
not  exceed  2.5  v.  (Compare  Fig.  33).  The  rule  establishing  a 
drop  of  1  v.  per  km.  states  that  the  current  in  the  track  must  not 

exceed  ===  if  W  is  the  resistance  of  the  track  in  ohms  per  km.  For 
a  uniform  load  of  a  section  of  L  km.  length  and  a  uniform  resistance, 
the  permissible  drop  in  potential  is  -^  v.  i.e.  one-half  the  drop  in 

one  rail.  The  calculation  of  this  drop  is  also  is  based  on  the 
average  load,  according  to  the  shedule. 

Strict  rules  have  been  issued  for  the  interior  rail  network  with 
its  many  branches,  as  it  mostly  covers  the  same  area  as  the  pipe 
network.  This  has  been  done  in  consideration  of  the  greater 
surface  of  contact  between  ground  and  rails  and  pipes,  respectively, 
which  increases  the  probability  of  a  passage  of  current  through 
the  ground.  The  potential  of  2.5  volts  for  this  district  has  been 
judged  permissible  because,  according  to  the  results  of  previous 
investigations,  it  is  to  be  assumed  that  this  potential  will  not 
under  ordinary  conditions  cause  any  danger  to  pipe  lines  beyond 
practical  limits.  To  avoid  as  much  as  possible  any  greater  con- 
centrations of  ground  and  pipe  currents  at  the  outlying  sections 
which  immediately  join  the  inner  rail  network,  and  where  im- 
portant parts  of  the  pipe  network  often  extend,  strict  rules  have 
been  issued  covering  the  district  inside  the  2  km.  belt  around  the 
inner  rail  network. 

For  the  outlying  section  an  economical  advantage  has  been 


168 


EUROPEAN  PRACTICE 


contemplated  by  limiting  the  drop  in  potential  to  1  v.  per  km. 
Railroads  interconnected  by  their  rail  networks  or  by  a  common 
power  plant  are  to  be  considered  as  one  system  because  such  rail- 


District  of  interior  pipe  •  network. 
District  of  200  m.  around  pipes  with  no  branches. 
Railroads  in  the  25  V.  District. 
Railroads  in  the  I  V-Km  District. 
Railroads  w«th  no  Restrictions. 
Fig.  32. 


District  of  the  pipe -network  with  the  200m:  belt 
surrounding  it  and  the  pipes  with  no  branches.; 
District  of  the  interior  Rail-network  with  Jjle£Kni., 
belt  surrounding  it 

Railroads  m  the  2/5  V.  District  (shaded  by  both 

horizontal  and  vertical  lines). 

—  —     Railroads  in  the  IV-Km  District  (shaded  by 
horizontal  lines) 

Railroads  with  no  restrictions  (not  shaded,  or  by 

vertical  lines  only> 

KEY  TO  CALCULATION  OP  VOLTAGE  DROP  IN  RAILS 
Fig.  33. 

roads  influence  each  other,  inasmuch  as  equalizing  currents  will 
flow  between  their  rail  networks. 

Deviations  in  both  directions  from  these  potentials  can  be 
justified  by  certain   circumstances — in  case  of  especially  good 


EUROPEAN  PRACTICE  169 

conditions  of  the  ground,  that  is  to  say,  in  very  dry  dirt  an  increase 
of  the  potentials  may  be  permissible.  But  even  in  such  cases  it  is 
advisable  to  be  cautious  in  allowing  such  an  increase,  so  as  not  to 
violate  the  rules  as  given  in  paragraph  5.  Where  the  conditions 
are  unfavorable,  for  instance,  where  moist  ground  of  especially 
high  conductivity  prevails,  it  is  advisable,  to  remain  below  the 
limits.  For  railroads  with  brief  daily  operation  concessions  have 
been  made  because  damage  to  the  pipes  depends  upon  the  dura- 
tion of  the  influence  of  the  current  so  that,  considering  the  short 
time  of  operation,  even  greater  currents  cannot  cause  any  appreci- 
able damage  to  the  pipes. 

For  railroads  of  three  hours  daily  operation  double  drop  in 
potential  is  allowed,  while  for  railroads  of  one  hour  operation, 
four  times  the  drop  is  permissible.  Wherever  the  rail  network 
is  not  sufficient  to  carry  the  current  without  exceeding  the  per- 
missible potential  in  the  network,  the  whole  plan  for  the  return 
of  the  current  must  be  altered,  and  improvement  will  be  reached 
by  providing  return  cables  in  which,  if  necessary,  resistances  or 
boosters  may  be  inserted.  The  resistances  should  be  variable  so 
as  to  correspond  with  the  variable  conditions  of  service  and  opera- 
tion. In  cases  where  the  railroad  system  is  fed  from  several 
power  plants  a  reduction  of  the  drop  in  potential  in  the  rails  may 
be  brought  about  by  shifting  the  loads  of  the  several  power  plants. 

The  arrangement  of  the  cables  and  resistances  can  be  made  in 
so  many  different  ways  as  to  make  a  general  rule  for  all  cases 
impossible.  It  is  recommended  to  investigate  thoroughly  the 
cases  under  observation,  because  considerable  saving  in  the  con- 
struction and  operation  of  the  plant  may  be  achieved  by  a  careful 
layout. 

The  keeping  of  the  return  points  at  the  same  potential  is  recom- 
mended as  a  precautionary  measure  but  not  required.  The  same 
offers  a  certain  guarantee  of  the  possibility  of  keeping  the  differ- 
ence of  potential  within  the  2.5  v.  limits. 

Furthermore,  the  use  of  the  three- wire  system  with  the  rails 
as  a  neutral  conductor  is  worthy  of  consideration.  In  this  system 
the  difference  of  potential  in  the  rails  depends  on  the  distribution 
of  the  positive  and  negative  feeder  districts.  This  distribution 
again  depends  on  the  local  conditions  of  the  plant,  so  that  no 
general  rules  can  be  given  in  regard  to  it. 

Alterations  of  the  conditions  of  operation  can  be  counteracted 
by  switching  the  load  to  the  positive  or  negative  side  of  the 
system.  The  rules  do  not  recommend  any  certain  system,  but 


170  EUROPEAN  PRACTICE 

leave  it  entirely  to  the  projecting  engineer  to  select  the  one  best 
adapted  to  existing  conditions.  The  damage  to  pipes  takes  place 
mostly  at  points  of  low  potential  on  two-wire  railroads,  in  the 
neighborhood  of  the  return  points ;  and  on  three- wire  railroads,  in 
the  districts  of  negative  feeders;  because  it  is  mainly  here  that 
the  current  leaves  the  pipes.  It  is  advisable  to  place  the  return 
points  of  the  negative  feeder  districts  whenever  possible  in  loca- 
tions with  dry  ground  of  low  conductivity  and  as  far  as  possible 
from  such  pipe  lines  as  are  of  importance  for.  the  water  and  gas 
supply. 

The  permissible  limits  of  differences  in  potential  in  rails  must 
not  exceed,  either  according  to  calculations  or  at  the  practical 
trial,  the  limits  given  in  Section  1,  of  these  rules.  The  measure- 
ment of  the  difference  in  potential  is  made  by  means  of  test 
wires  as  called  for  in  Section  6.  The  measurements  of  differences 
in  potential  are  limited  to  those  points  which,  according  to  calcu- 
lations, come  nearest  to  the  established  limits.  Wherever  long 
lines,  as,  for  instance,  telephone  wires,  are  available,  it  is  advisable 
to  use  them  for  these  measurements  otherwise  several  test  wires 
may  be  connected  in  series  or  temporary  test  lines  may  be  in- 
stalled. Finally,  the  restilts  of  single  measurements  may  be 
computed  to  reach  the  same  final  results.  Only  high  resistance 
voltmeters  should  be  used  for  these  measurements  so  as  to  make 
the  resistances  of  the  test  wire  and  .contacts  negligible.  The 
pointers  of  these  instruments  should  have  the  slowest  movements 
and  a  good  damper  arrangement,  so  as  to  give  good  readings  even 
under  strong  fluctuations.  For  all  measurements  only  average 
values  are  considered.  All  measurements  are  to  be  extended 
over  a  full  period  of  operation  which  results  from  the  average 
frequency  of  trains. 

Section  4.     Resistance  Between  Rail  and  Earth 

The  resistance  between  ground  and  the  rail  which  is  used  for 
carrying  the  return  current  should  be  kept  as  high  as  possible. 
When  the  conditions  of  the  ground  or  the  situation  of  the  track 
are  not  favorable  for  this  purpose,  the  resistance  should  be  in- 
creased by  a  special  effective  insulation. 

The  rails  or  any  conductor  connected  to  the  rails  must  not  be 
in  contact  with  the  pipes  or  any  kind  of  metal  buried  in  the 
ground.  Furthermore,  care  must  be  taken  that  the  distance 
between  the  nearest  rail  and  any  metallic  part  of  the  pipe  lines 
or  connections  to  them  which  project  above  the  ground  or  lie 


EUROPEAN  PRACTICE  171 

near  the  surface,  be  kept  as  great  as  possible,  and  should  never 
be  less  than  one  meter. 

Stationary  motors,  lighting  installations  or  any  other  plant 
which  receives  current  from  a  railway  system  which  uses  the  rails 
for  carrying  the  return  current,  must  be  connected  to  the  rail 
network  by  means  of  insulated  conductors.  Excepted  are  short 
connections  of  not  more  than  16  square  millimeters  which  are  not 
deeper  than  25  centimeters  in  the  ground  and  which  are  at  a  dis- 
tance of  at  least  1  meter  from  any  part  of  a  pipe  network.  These 
connections  may  be  of  bare  metal.  In  order  to  increase  the  resist- 
ance between  rail  and  ground  it  is  recommended  to  use  a  bedding 
of  high  resistance  and  to  provide  good  drainage,  also  to  render 
the  bedding  water-tight  to  the  roadbed  for  a  sufficient  width  on 
both  sides  of  the  rail. 

The  use  of  salt  for  the  melting  of  snow  and  ice,  should  be  limited 
to  cases  of  absolute  necessity. 

Wherever  sufficient  distance  between  the  rail  and  such  parts  of 
the  pipe  line  as  project  above  the  surface  is  not  obtainable,  it  is 
advisable  to  change  the  pipe  run,  or  where  this  is  not  possible,  to 
use  insulating  strata  (such  as  vitrified  clay,  masonry  or  wooden 
conduits,  etc. 

Explanation 

The  magnitude  of  currents  passing  into  the  ground  depends 
not  only  on  the  potentials  in  the  rail  network,  but  also  on  the 
resistances  between  the  rails  and  the  pipes  and  on  the  resistances 
of  the  pipe  lines  themselves.  It  will  always  be  of  advantage  to 
increase  the  resistance  of  the  ground  between  the  rails  and  the 
pipes.  An  artificial  increase  of  the  resistances  of  the  pipe  line 
can  'be  achieved  for  instance,  by  the  use  of  insulating  flanges, 
couplings,  etc.  Aside  from  the  technical  difficulties  of  installing 
such  insulating  parts  into  gas  pipes,  and  especially  water  pipes 
with  a  high  pressure,  and  of  insuring  their  lasting  tightness,  it 
would  be  difficult  to  provide  these  insulating  pieces  in  the  necessary 
numbers  and  to  take  care  of  their  correct  distribution.  A  wrong 
arrangement  of  the  same  will  lead  to  an  extraordinary  concentra- 
tion of  currents  at  these  insulations  with  consequent  corrosion  in 
these  places.  A  greater  part  of  the  drop  in  potential  between 
pipe  and  rail  originally  takes  place  in  the  roadbed  as  can  be  easily 
understood  and  it  is  therefore  required  to  render  this  resistance 
as  high  as  possible  by  the  good  insulation  of  the  roadbed,  good 
drainage,  etc.,  and  to  maintain  it  thus. 


172  EUROPEAN  PRACTICE 

In  the  same  measure  that  the  increase  of  the  resistances  between 
rail  and  pipe  is  recommended,  the  use  of  any  means  to  reduce  these 
resistances,  is  to  be  warned  against.  Such  means  to  be  considered 
are  ground  plates,  connections  of  metals  in  the  ground,  and  espe- 
cially metallic  connections  between  the  rails  and  the  pipes.  The 
last  will  reduce  the  density  of  the  current  at  the  point  of  connec- 
tion to  the  pipe,  but  they  cause  an  increase  of  the  pipe  current  and 
of  the  ground  currents  in  general  which  may  cause  damage  in 
other  places,  as,  for  instance,  at  interruptions  in  the  pipe  line  or 
at  crossings  with  other  lines.  Any  local  measure  taken  must  be 
considered  with  regard  to  its  effect  on  the  pipes  in  other  localities. 

Metallic  connections  between  different  pipe  networks  also  are 
to  be  judged  from  this  viewpoint.  Immediate  contact  of  any 
parts  of  the  pipe  lines  with  the  rails,  or  too  close  an  approach,  has 
the  same  effect  as  direct  metallic  connections  and  is,  therefore,  to 
be  avoided.  (By  a  relocation  of  rails  or  pipes  or  installation  of 
insulating  strata). 

Especially  in  cases  of  stationary  motors  or  lighting  plants 
connected  to  the  railroad  system,  there  exists  on  the  premises 
danger  of  an  accidental  or  deliberate  connection  or  contact  with 
the  pipe  lines.  It  is,  therefore,  necessary  to  have  strict  rules 
regarding  the  return  cables  from  such  plants. 

Section  5.     Current  Density 

The  above  rules  are  intended  to  prevent  the  destruction  of  the 
pipes  by  electrolysis.  The  rate  of  destruction  is  in  direct  propor- 
tion to  the  amount  of  current  leaving  the  pipe. 

Any  pipe  line  where  the  current  leaving  the  pipe  exceeds  an 
average  density  of  0.75  milliampere  per  square  decimeter  and 
where  this  current  is  due  to  a  railway,  may  be  considered  en- 
dangered by  this  railway,  and  further  preventive  measures  must 
be  taken. 

For  railways  with  freight  service  when  the  service  is  of  com- 
paratively short  duration,  exceptions  as  already  mentioned  are 
permissible. 

In  cases  where  the  current  leaving  or  passing  into  the  pipes 
changes  its  direction,  the  current  passing  into  the  pipe  must  be 
taken  as  nil  when  determining  the  average  density,  until  further 
experience  has  been  gained  in  this  matter. 

Explanation 

Inasmuch  as  a  total  elimination  of  all  damages  to  pipes  would 
be  in  most  cases  possible  only  at  a  disproportionately  high  cost, 


EUROPEAN  PRACTICE  173 

which  would  far  exceed  the  cost  of  any  possible  damage  to  the 
pipes,  it  is  necessary  to  allow  a  certain  limited  damage,  that  is  to 
say,  a  damage  which  is  of  little  practical  importance  and  which 
does  not  noticeably  shorten  the  life  of  the  pipes.  These  rules 
have  therefore  been  compiled  on  the  basis  of  the  average  conditions, 
that  is  to  say,  such  as  are  mostly  met  with,  and  it  is  to  be  expected 
according  to  previous  experience  that  the  damage  done  to  pipe 
lines  by  the  stray  currents  from  electrical  railways  generally  will 
remain  limited  to  the  practical  allowable  limit  wherever  these  rules 
are  observed.  Under  exceptionally  bad  conditions,  that  is  to  say, 
under  conditions  which  very  much  favor  the  origin  of  stray  cur- 
rents, greater  corrosion  of  pipes  in  certain  places  can  hardly  be 
avoided,  even  if  the  limits  of  the  drop  in  the  potential  in  the  rails, 
as  laid  down  in  Section  3,  are  not  exceeded.  It  is,  therefore 
advisable  to  establish  some  measure  for  the  elimination  of  imme- 
diate danger  to  the  pipes. 

For  the  judgment  of  the  damage  attributed  to  a  railroad  system 
the  density  of  the  current  leaving  the  pipes  and  returning  to  the 
railroad  system  is  indicative. 

The  density  of  the  current  at  the  pipe  can  be  measured  only 
after  the  completion  of  the  plant.  These  measurements  must  be 
made  during  the  time  of  operation,. as  per  schedule,  and  as  de- 
scribed in  Section  3.  The  average  density  is  important  and  is 
obtained  from  the  computation  of  the  results  of  several  measure- 
ments, each  of  which  follows  a  whole  period  of  service. 

Measurements  of  current  density  can  be  made,  for  instance, 
by  means  of  a  milliammeter  and  non-polarizable  frame  as  designed 
by  Prof.  Haber.  This  frame  contains  two  copper  plates  which  are 
insulated  from  each  other  and  which  for  the  prevention  of  polariza- 
tion are  covered  with  a  paste  of  copper  sulphate  and  20  per  cent 
sulphuric  acid,  over  which  a  parchment,  soaked  with  sodium  sul- 
phate is  laid.  The  frame  is  filled  with  dirt  except  between  the 
plates,  and  placed  alongside  the  pipe  at  right  angles  to  the  as- 
sumed direction  of  the  current  and  then  covered  with  dirt.  A 
very  sensitive  ammeter  connected  to  the  copper  plates  will  indi- 
cate the  current  passing  through  the  frame  and  the  density  of 
this  current  can  readily  be  calculated  by  taking  into  account  the 
surface  of  the  copper  plates  inside  the  frame.  Inasmuch  as  here 
also  only  average  readings  are  to  be  considered,  it  is  advisable  to 
use  an  instrument  with  very  slow  period. 

According  to  investigations  made  so  far,  absolute  danger  to  the 
pipes  results  whenever  the  density  of  the  currents  leaving  the 


174  EUROPEAN  PRACTICE 

pipes  reaches  the  average  value  of  0.75  milliampere  per  square 
decimeter.  For  railroads  with  small  periods  of  operation  an  excess 
up  to  double  and  quadruple,  respectively,  the  above  value  is 
permissible  according  to  the  rules  laid  down  in  Section  3. 

Wherever  the  direction  of  the  current  changes,  the  current 
entering  the  pipes  are  not  to  be  considered  in  the  calculations 
of  the  average  density,  inasmuch  as  it  is  not  yet  established  that 
such  currents  will  add  to  the  metal  of  the  pipes.  Wherever  the 
average  values  are  exceeded,  special  precautionary  measures 
are  to  be  taken,  the  nature  of  which  can  be  determined  only  by 
the  local  conditions.  In  many  cases  it  is  sufficient  to  protect  a 
very  limited  section  of  the  rail  network,  to  which  end  the  further 
reduction  of  the  drop  in  the  rails  may  not  be  necessary,  but  which 
may  be  attained  by  other  means  as,  for  instance,  the  re-location 
of  short  sections  of  tracks  or  pipes,  or  the  artificial  increase  of  the' 
resistances  between  rails  and  pipes  at  such  points. 

In  all  cases  the  question  arises  whether  the  railroad  is  to  be 
considered  as  the  only  cause  of  current  concentration,  as  other 
causes  may  be  found  to  be  responsible  for  a  part  of  the  current 
on  the  pipes;  for  instance,  bare  neutrals  or  poor  insulation  in 
other  electrical  systems,  the  natural  electrical  elements  resulting 
from  the  use  of  different  metals  in  the  pipe  lines,  or  from  different 
chemicals  in  solution  in  the  ground.  That  part  of  the  current 
which  is  attributable  to  the  influence  of  the  railroad  can  be  deter- 
mined by  comparison  with  the  measurements  of  the  current 
during  the  period  of  no  operation.  In  many  cases  the  influence 
of  the  railroad  can  be  judged  from  contemporaneous  measurements 
of  current  density  and  the  potential  between  pipe  and  rail.  Under 
certain  circumstances  it  is  possible  to  find  the  degree  of  influence 
of  the  railroad  and  of  other  electrical  plants  operating  at  the 
same  time,  by  establishing  the  course  of  the  current  in  the  ground. 
For  this  investigation  electrodes  that  cannot  be  polarized  are  used 
as  contacts  from  the  test  line  to  the  ground.  The  measurements 
should  preferably  be  made  by  the  potentiometer  method  in  order 
to  eliminate  drop  at  the  electrodes  due  to  the  current  flow,  but 
this  method  is  difficult  in  practice  on  account  of  the  rapid  fluctua- 
tions of  the  voltage.  It  will  be  sufficient  in  most  cases  to  make 
the  measurements  with  a  voltmeter  of  very  high  resistance  so  that 
the  current  passing  through  the  electrodes  will  be  very  small. 
It  should  be  emphasized  that  such  measurements  should  be  made 
by  experts  only,  as  deviations  from  the  right  method  which  seem 
of  no  importance  often  give  useless  results. 


EUROPEAN  PRACTICE  175 

Section  6.     Control. 

In  order  to  be  able  to  test  the  potential  at  the  return  points  of 
the  rail  system  of  a  given  territory,  pilot  wires  are  to  be  connected 
to  these  points  and  carried  to  a  central  testing  place. 

Before  a  service  may  be  increased  the  potential  distribution  in 
the  rail  network  must  be  retested. 

The  rail  bonds  and  bridge  connections  are  to  be  retested  once 
yearly  by  means  of  a  suitable  rail  joint  tester  and  must  be  ar- 
ranged so  that  they  fulfill  the  rules  of  Sections  1  and  2.  Con- 
nections, the  resistance  of  which  has  been  found  greater  than  that 
of  an  uninterrupted  rail  of  ten  meters  length,  must  be  repaired 
to  comply  with  these  rules. 

Explanation. 

The  control  of  the  drop  in  potential  in  the  whole  network  would 
be  best  assured  by  the  installation  of  test  wires  from  one  of  the 
buses  to  all  points  of  probable  highest  and  lowest  rail  potential, 
which  arrangement  admits  of  immediate  measurement  of  poten- 
tial between  these  points. 

In  certain  cases,  especially  in  existing  plants,  the  installation 
of  such  test  wires  would  involve  great  cost.  Such  test  wires  from 
all  of  the  important  rail  points  were  not  required;  but  it  has  been 
ruled  that  all  points  of  the  rail  network,  to  which  cables  of  the 
same  district  are  now  connected,,  are  to  be  provided  with  test 
wires  which  have  to  run  to  some  central  point  where  readings  of 
the  differences  of  potentials  between  the  return  points  can  be 
taken. 

Wherever  the  expense  involved  permits,  it  is  recommended  to 
install  test  wires  not  only  to  the  return  points  but  also  to  the 
points  of  highest  rail  potentials. 

After  permanent  changes  in  the  operation,  the  distribution  of 
the  potential  in  the  rail  network  is  to  be  investigated  in  the  same 
way  as  after  the  inauguration  of  the  plant,  in  order  to  ascertain 
whether  the  new  conditions  still  correspond  to  the  rules. 

In  case  of  temporary  changes  of  short  duration  in  the  whole 
network  or  parts  of  the  same  as,  for  instance,  occasionally  some 
festival,  change  or  repair  of  tracks,  fairs,  exhibits,  etc.,  no  special 
measures  are  to  be  taken  because  the  short  duration  of  the  influ- 
ence will  cause  no  noticeable  damage  even  when  the  limits  of 
these  rules  are  exceeded. 

The  yearly  investigation  of  the  rail  joints,  as  required  by  the 
rules,  is  also  to  be  recommended  with  regard  to  the  reduction  of 


176  EUROPEAN  PRACTICE 

losses  of  energy.  For  these  measurements  an  apparatus  may  be 
used  which  allows  of  the  comparison  of  the  drop  in  potentials 
across  the  joint  with  one  of  the  adjoining  uninterrupted  rails  so 
that  the  measurement  may  be  taken  during  the  operation.  Joints 
of  a  resistance  higher  than  that  of  an  uninterrupted  rail  of  10  m. 
length  are  immediately  to  be  repaired.  The  total  resistance,  as 
found  by  the  measurement  of  the  single  joints,  must  not  exceed 
the  value  which  has  been  assumed  during  the  projection  of  the 
plant  (compare  Section  2,  paragraph  2). 

Should  it  result  during  operation  that  rail  joints  are  of  a  higher 
resistance  than  that  assumed  in  the  designing,  it  is  permissible 
to  abstain  from  a  reconstruction  of  the  joints  as  long  as  the 
permissible  difference  of  potentials  in  the  rails  is  not  exceeded, 
even  with  these  higher  resistances.  The  established  limits  of 
20%  increase  of  the  resistance  of  the  uninterrupted  rail  by  the 
bonds  must  not  be  exceeded  in  any  case. 

FRANCE— REGULATIONS  BY  MINISTER  OF  PUBLIC  WORKS 

CIRCULAR  AND  ORDER  OF  THE  MINISTER  OF  PUBLIC  WORKS  (FRANCE)  OF 
MARCH  21,  1911,  ESTABLISHING  THE  TECHNICAL  CONDITIONS  WHICH  ELECTRICAL 
DISTRIBUTION  SYSTEMS  MUST  SATISFY  IN  ORDER  TO  CONFORM  TO  THE  LAW  OF 
JUNE  15,  1906. 

Regulations  Relative  to  the  Construction  of  Structures  for  Electric  Railways 
Using  Direct  Currents. 

Right  of  Way. 

When  the  rails  are  used  as  conductors,  all  necessary  measures 
should  be  taken  to  guard  against  the  harmful  action  of  stray  cur- 
rents, on  metallic  structures,  such  as  the  tracks  of  railways,  the 
water  and  gas  pipes,  the  telegraph  or  telephone  lines  and  all  other 
electric  conductors,  etc. 

To  this  end  the  following  regulations  shall  be  applied: 

1.  The  conductance  of  the  tracks  shall  be  known  to  be  in  the 
best  possible  condition,  especially  in  regard  to  the  joints,  whose 
resistance  should  not  exceed,  in  each  case,  that  of  10  meters  of 
the  normal  track. 

The  management  is  required  to  verify  periodically  this  con- 
ductance and  to  place  the  results  obtained  on  file,  which  shall  be 
accessible  to  the  administration  upon  demand. 

2.  The  drop  in  potential  in  the  rails,  measured  upon  a  length 
of  track  of  1  kilometer  taken  arbitrarily  upon  any  section  of  the 
system,  should  not  exceed  an  average  value  of  1  volt  for  the  operat- 
ing period  of  the  normal  car  schedule. 

3.  The  feeders  tied  into  the  track  shall  be  insulated. 


EUROPEAN  PRACTICE  177 

4.  Where  the  tracks  contain  switches  or  crossings,  the  conduct- 
ance shall  be  maintained  by  special  work. 

5.  When  the  track  crosses  a  metallic  structure,  it  should  be 
electrically  insulated,  as  much  as  possible,  throughout  the  length 
of  the  structure. 

6.  As  long  as  no  metallic  structure  is  in  the  neighborhood  of  the 
tracks,  a  drop  in  potential  greater  than  that  fixed  in  paragraph 
2  may  be  allowed,  upon  the  condition  that  no  damage  will  result, 
and  particularly  no  trouble  to  telegraphic  or  telephonic  communi- 
cation, and  none  to  railway  signals. 

7.  The  owner  of  the  distribution  system  shall  be  required  to 
make  the  installations  necessary  to  enable  the  administration  to 
verify  the  fulfillment  of  the  provisions  of  this  article;  it  should 
particularly  provide,  whenever  necessary,  for  pilot  wires  to  be 
installed  between  designated  points  of  the  distribution  system. 

Protection  oj  Neighboring  Aerial  Lines 

At  all  points  where  the  lines  feeding  the  traction  system  cross 
other  distribution  lines,  or  telegraph  or  telephone  lines,  the  sup- 
ports should  be  established  with  a  view  to  protect  mechanically 
these  lines  against  contact  with  the  aerial  conductors  feeding  the 
traction  system. 

In  all  cases,  measures  shall  be  taken  to  prevent  the  trolley  wire 
touching  the  neighboring  lines. 

ENGLAND— BRITISH  BOARD  OF  TRADE  REGULATIONS 

REGULATIONS  MADE  BY  THE  BOARD  OF  TRADE  UNDER  THE  PROVISIONS  OF 
SPECIAL  TRAMWAYS  ACTS  OR  LIGHT  RAILWAY  ORDERS  AUTHORIZING  "LINES" 
ON  PUBLIC  ROADS;  FOR  REGULATING  THE  USE  OF  ELECTRICAL  POWER;  FOR 
PREVENTING  FUSION  OR  INJURIOUS  ELECTROLYTIC  ACTION  OF  OR  ON  GAS  OR 
WATER  PIPES  OR  OTHER  METALLIC  PIPES,  STRUCTURES  OR  SUBSTANCES;  AND 
FOR  MINIMIZING  AS  FAR  AS  IS  REASONABLY  PRACTICABLE  INJURIOUS  INTERFER- 
ENCE WITH  THE  ELECTRIC  WIRES,  LINES,  AND  APPARATUS  OF  PARTIES  OTHER 
THAN  THE  COMPANY,  AND  THE  CURRENTS  THEREIN,  WHETHER  SUCH  LINES  DO 
OR  DO  NOT  USE  THE  EARTH  AS  A  RETURN. 

FIRST  MADE,  MARCH,  1894. 

REVISED,  APRIL,  1903. 

FURTHER  REVISED,  AUGUST,  1904. 

FURTHER  REVISED,  MAY,  1908. 

FURTHER  REVISED,  APRIL,  1910. 

FURTHER  REVISED,  SEPTEMBER,  1912. 

Regulations 

1.  Any  dynamo  used  as  a  generator  shall  be  of  such  pattern 
and  construction  as  to  be  capable  of  producing  a  continuous 
current  without  appreciable  pulsation. 


178  EUROPEAN  PRACTICE 

2.  One  of  the  two  conductors  used  for  transmitting  energy  from 
the  generator  to  the  motors  shall  be  in  every  case  insulated  from 
earth,  and  is  hereinafter  referred  to  as  the  "line";  the  other  may 
be  insulated  throughout,  or  may  be  uninsulated  in  such  parts  and 
to  such  extent  as  is  provided  in  the  following  regulations,  and  is 
hereinafter  referred  to  as  the  "return." 

NOTE:  The  Board  of  Trade  will  be  prepared  to  consider 
the  issue  of  regulations  for  the  use  of  alternating  currents  for 
electrical  traction  on  application. 

3.  Where  any  rails  on  which  cars  run  or  any  conductors  laid 
between  or  within  three  feet  of  such  rails  form  any  part  of  a  return, 
such  part  may  be  uninsulated.     All  other  returns  or  parts  of  a 
return  shall  be  insulated,  unless  of  such  sectional  area  as  will  re- 
duce the  difference  of  potential  between  the  ends  of  the  uninsulated 
portion  of  the  return  below  the  limit  laid  down  in  Regulation  7. 

4.  When  any  uninsulated  conductor  laid  between  or  within 
three  feet  of  the  rails  forms  any  part  of  a  return,  it  shall  be  elec- 
trically connected  to  the  rails  at  distances  apart  not  exceeding 
100  feet  by  means  of  copper  strips,  having  a  sectional  area  of  at 
least  one-sixteenth  of  a  square  inch,  or  by  other  means  of  equal 
conductivity. 

5.  (a)  When  any  part  of 'a  return  is  uninsulated  it  shall  be 
connected  with  the  negative  terminal  of  the  generator,  and  in 
such  case  the  negative  terminal  of  the  generator  shall  also  be 
directly    connected,    through    the    current-indicator    hereinafter 
mentioned,  to  two   separate    earth    connections  which  shall  be 
placed  not  less  than  20  yards  apart. 

(b)  The  earth  connections  referred  to  in  this  regulation  shall 
be  constructed,  laid  and  maintained,  so  as  to  secure  electrical 
contact  with  the  general  mass  of  earth,  and  so  that,  if  possible, 
an  electromotive  force,  not  exceeding  four  volts,  shall  suffice  to 
produce  a  current  of  at  least  two  amperes  from  one  earth  con- 
nection to  the  other  through  the  earth,  and  a  test  shall  be  made 
once  in  every  month  to  ascertain  whether  this  requirement  is 
complied  with. 

(c)  Provided  that  in  place  of  such  two  earth  connections  the 
Company  may  make  one  connection  to  a  main  for  water  supply 
of  not  less  than  three  inches  internal  diameter,  with  the  consent 
of  the  owner  thereof,  and  of  the  person  supplying  the  water,  and 
provided  that  where,  from  the  nature  of  the  soil  or  for  other 
reasons,  the  Company  can  show  to  the  satisfaction  of  the  Board 
of  Trade  that  the  earth  connections  herein  specified  cannot  be 


EUROPEAN  PRACTICE  179 

constructed  and  maintained  without  undue  expense,  the  provi- 
sions of  this  regulation  shall  not  apply. 

(d)  No  portion  of  either  earth  connection  shall  be  placed  within 
six  feet  of  any  pipe  except  a  main  for  water  supply  of  not  less  than 
three  inches  internal  diameter,  which  is  metallically  connected  to 
the  earth  connections  with  the  consents  hereinbefore  specified. 

(e)  When  the  generator  is  at  a  considerable  distance  from  the 
tramway  the  uninsulated  return  shall  be  connected  to  the  negative 
terminal  of  the  generator  by  means  of  one  or  more  insulated  return 
conductors,  and  the  generator  shall  have  no  other  connection  with 
earth ;  and  in  such  case  the  end  of  each  insulated  return  connected 
with  the  uninsulated  return  shall  be  connected  also  through  a 
current  indicator  to  two  separate  earth  connections,  or  with  the 
necessary  consents  to  a  main  for  water  supply,  or  with  the  like 
consents  to  both  in  the  manner  prescribed  in  this  regulation. 

(/)  The  current  indicator  may  consist  of  an  indicator  at  the 
generating  station  connected  by  insulated  wires  to  the  terminals 
of  a  resistance  interposed  between  the  return  and  the  earth  con- 
nection or  connections,  or  it  may  consist  of  a  suitable  low-resist- 
ance maximum  demand  indicator.  The  said  resistance,  or  the 
resistance  of  the  maximum  demand  indicator,  shall  be  such  that 
the  maximum  current  laid  down  in  Regulation  6  (I)  shall  produce 
a  difference  of  potential  not  exceeding  one  volt  between  the  ter- 
minals. The  indicator  shall  be  so  constructed  as  to  indicate  cor- 
rectly the  current  passing  through  the  resistance  when  connected 
to  the  terminals  by  the  insulated  wires  before-mentioned. 

6.  When  the  return  is  partly  or  entirely  uninsulated  the  Com- 
pany shall  in  the  construction  and  maintenance  of  the  tramway 
(a)  so  separate  the  uninsulated  return  from  the  general  mass  of 
earth,  and  from  any  pipe  in  the  vicinity;  (b)  so  connect  together 
the  several  lengths  of  the  rails ;  (c)  adopt  such  means  for  reducing 
the  difference  produced  by  the  current  between  the  potential  of 
the  uninsulated  return  at  any  one  point  and  the  potential  of  the 
uninsulated  return  at  any  other  point;  and  (d)  so  maintain  the 
efficiency  of  the  earth  connections  specified  in  the  preceding  regu- 
lations as  to  fulfill  the  following  conditions,  viz: 

(I)  That  the  current  passing  from  the  earth  connections 
through  the  indicator  to  the  generator  or  through  the  resist- 
ance to  the  insulated  return  shall  not  at  any  time   exceed 
either  two  amperes  per  mile  of  single  tramway  line  or  five 
per  cent  of  the  total  current  output  of  the  station. 

(II)  That  if  at  any  time  and  at  any  place  a  test  be  made 


180  EUROPEAN  PRACTICE 

by  connecting  a  galvanometer  or  other  current-indicator  to 

the  uninsulated  return  and  to  any  pipe  in  the  vicinity,  it  shall 

always  be  possible  to  reverse  the  direction  of  any  current 

indicated  by  interposing  a  battery  of  three  Leclanche  cells 

connected  in  series  if  the  direction  of  the  current  is  from  the 

return  to  the  pipe,  or  by  interposing  one  Leclanche  cell  if  the 

direction  of  the  current  is  from  the  pipe  to  the  return. 

The  owner  of  any  such  pipe  may  require  the  Company  to  permit 

him  at  reasonable  times  and  intervals  to  ascertain  by  test  that  the 

conditions  specified  in  (II)  are  complied  with  as  regards  his  pipe. 

7.  When  the  return  is  partly  or  entirely  uninsulated  a  con- 
tinuous record  shall  be  kept  by  the  Company  of  the  difference  of 
potential  during  the  working  of  the  tramway  between  points  on 
the  uninsulated  return.     If  at  any  time  such  difference  of  potential 
between  any  two  points  exceeds  the  limit  of  seven  volts,  the  Com- 
pany shall  take  immediate  steps  to  reduce  it  below  that  limit. 

8.  The  current  density  in  the  rails  shall  not  exceed  nine  am- 
peres per  square  inch  of  the  cross-sectional  area. 

9.  Every  electrical  connection  with  any  pipe  shall  be  so  arranged 
as  to  admit  of  easy  examination,  and  shall  be  tested  by  the  Com- 
pany at  least  once  in  every  three  months. 

10.  Trie  insulation  of  the  line  and  of  the  return  when  insulated, 
and  of  all  feeders  and  other  conductors,  shall  be  so  maintained 
that  the  leakage  current  shall  not  exceed  one  hundredth  of  an 
ampere  per  mile  of  tramway.     The  leakage  current  shall  be  as- 
certained not  less  frequently  than  once  in  every  week  before  or 
after  the  hours  of  running  when  the  line  is  fully  charged.     If  at 
any  time  it  should  be  found  that  the  leakage  current  exceeds  one- 
half  of  an  ampere  per  mile  of  tramway,  the  leak  shall  be  localized 
and  removed  as  soon  as  practicable,  and  the  running  of  the  cars 
shall  be  stopped  unless  the  leak  is  localized  and  removed  within 
24  hours.     Provided  that  where  both  line  and  return  are  placed 
within  a  conduit  this  regulation  shall  not  apply. 

11.  The  insulation  resistance  of  all  continuously  insulated  cables 
used  for  lines,  for  insulated  returns,  for  feeders,  or  for  other  pur- 
poses, and  laid  below  the  surface  of  the  ground,  shall  not  be  per- 
mitted to  fall  below  the  equivalent  of  10  megohms  for  a  length 
of  one  mile.     A  test  of  the  insulation  resistance  of  all  such  cables 
shall  be  made  at  least  once  in  each  month. 

12.  Any  insulated  return  shall  be  placed  parallel  to  and  at  a 
distance  not  exceeding  three  feet. from  the  line  when  the  line  and 


EUROPEAN  PRACTICE  181 

return  are  both  erected  overhead,  or  eighteen  inches  when  they 
are  both  laid  underground. 

13.  In  the  disposition,   connections,  and  working  of  feeders, 
the  Company  shall  take  all  reasonable  precautions  to  avoid  in- 
jurious interference  with  any  existing  wires. 

14.  The  Company  shall  so  construct  and  maintain  their  sys- 
tem as  to  secure  good  contact  between  the  motors  and  the  line  and 
return,  respectively. 

15.  The  Company  shall  adopt  the  best  means  available  to 
prevent  the  occurrence  of  undue  sparking  at  the  rubbing  or  rolling 
contacts  in  any  place  and  in  the  construction  and  use  of  their 
generator  and  motors. 

16.  Where  the  line  or  return  or  both  are  laid  in  a  conduit  the 
following  conditions  shall  be  complied  with  in  the  construction 
and  maintenance  of  such  conduit. 

(a)  The  conduit  shall  be  so  constructed  as  to  admit  of 
examination  of  and  access  to  the  conductors  contained  therein 
and  their  insulators  and  supports. 

(b)  It  shall  be  so  constructed  as  to  be  readily  cleared  of 
accumulation  of  dust  or  other  debris,  and  no  such  accumula- 
tion shall  be  permitted  to  remain. 

(c)  It  shall  be  laid  to  such  falls  and  so  connected  to  sumps 
or  other  means  of  drainage,  as  to  automatically  clear  itself 
of  water  without  danger  of  the  water  reaching  the  level  of  the 
conductors. 

(d)  If  the  conduit  is  formed  of  metal,  all  separate  lengths 
shall  be  so  jointed  as  to  secure  efficient  metallic  continuity  for 
the  passage  of  electric  currents.     Where  the  rails  are  used  to 
form  any  part  of  the  return  they  shall  be  electrically  connected 
to  the  conduit  by  means  of  copper  strips  having  a  sectional 
area  of  at  least  one-sixteenth  of  a  square  inch,  or  other  means 
of  equal  conductivity,  at  distances  apart  not  exceeding  100 
feet.     Where  the  return  is  wholly  insulated  and  contained 
within  the  conduit,  the  latter  shall  be  connected  to  earth  at 
the  generating  station  or  sub-station  through  a  high  resistance 
galvanometer  suitable  for  the  indication  of  any  contact  or 
partial  contact  of  either  the  line  or  the  return  with  the  conduit. 

(e)  If  the  conduit  is  formed  of  any  non-metallic  material 
not  being  of  high  insulating  quality  and  impervious  to  mois- 
ture throughout,  the  conductors  shall  be  carried  on  insulators, 
the  supports  for  which  shall  be  in  metallic  contact  with  one 
another  throughout. 


182  EUROPEAN  PRACTICE 

(/)  The  negative  conductor  shall  be  connected  with  earth 
at  the  station  by  a  voltmeter  and  may  also  be  connected  with 
earth  at  the  generating  station  or  substation  by  an  adjust- 
able resistance  and  current-indicator.  Neither  conductor 
shall  otherwise  be  permanently  connected  with  earth. 

(g)  The  conductors  shall  be  constructed  in  sections  not 
exceeding  one-half  a  mile  in  length,  and  in  the  event  of  a  leak 
occurring  on  either  conductor  that  conductor  shall  at  once 
be  connected  with  the  negative  pole  of  the  dynamo,  and  shall 
remain  so  connected  until  the  leak  can  be  removed. 

(h)  The  leakage  current  shall  be  ascertained  daily,  before 
or  after  the  hours  of  running,  when  the  line  is  fully  charged 
and  if  at  any  time  it  shall  be  found  to  exceed  one  ampere  per 
mile  of  tramway,  the  leak  shall  be  localized  and  removed  as 
soon  as  practicable,  and  the  running  of  the  cars  shall  be 
stopped  unless  the  leak  is  localized  and  removed  within  24 
hours. 

17.  The  Company  shall,  so  far  as  may  be  applicable  to  their 
system  of  working,  keep  records  as  specified  below.  These  records 
shall,  if  and  when  required,  be  forwarded  for  the  information  of 
the  Board  of  Trade. 

Number  of  cars  running. 

Number  of  miles  of  single  tramway  line. 

Daily  Records. 

Maximum  working  current. 

Maximum  working  pressure. 

Maximum  current  from  the  earth  plates  or  water-pipe  connec- 
tions (vide  Regulation  6  (&))  where  the  indicator  is  at  the  generat- 
ing works. 

Fall  of  potential  in  return  (vide  Regulation  7). 

Leakage  current  (vide  Regulation  16  (h)). 

Weekly  Records. 

Leakage  current  (vide  Regulation  10). 

Maximum  current  from  the  earth  plates  or  water-pipe  connec- 
tions (vide  Regulations  6  (I))  where  a  maximum  demand  indicator 
is  used. 

Monthly  Records. 

Condition  of  earth  connections  (vide  Regulation  5) . 
Minimum  insulation  resistance  of  insulated  cables  in  megohms 
per  mile  (vide  Regulation  11). 


EUROPEAN  PRACTICE  183 

Quarterly  Records. 

Conductance  of  connections  to  pipes  (vide  Regulation  9). 
Occasional  Records. 

Specimens  of  test  made  under  provisions  of  Regulation  6  (II). 
Board  of  Trade, 

7,  Whitehall  Gardens,  S.  W.     September,  1912. 

SPAIN— ELECTRIC  LEGISLATION 

LAW  OF  MARCH  23,  1900. 

TO  PREVENT  THE  RETURN  CURRENT  OF  ELECTRIC  TRAMWAY  LINES  FROM 
EXERCISING  ANY  ELECTROLYTIC  EFFECTS,  THE  FOLLOWING  MEASURES  SHALL  BE 
TAKEN: 

(1)  The  rails  of  each  one  of  the  tracks  are  bonded  by  weld- 
ing or  by  connections  formed  of  short  copper  cables  or  of 
equivalent  cables  made  of  some  other  metal,  the  section  of 
which  having  to  exceed  100  square  millimeters  per  track,  and 
shall  be  made  as  large  as  possible. 

(2)  At  intervals  of  100  meters,  or  at  shorter  distances  the 
tracks  shall  be  cross-bonded. 

(3)  In  case  the  official  inspector  should  deem  it  necessary, 
a  cable  will  have  to  be  stretched  in  every  line,  which  will 
have  to  be  intimately  connected  with  both  tracks,  and 

(4)  The  dimensions  of  all  cables  and  wires  constituting 
such  system  will  have  to  be  calculated  upon  a  basis  that  the 
potential  difference  between  the  generator  terminals  and  the 
point  of  the  tracks  remotest  from  them  will  not  exceed  an 
amount  of  seven  volts. 


CHAPTER  5. 
ELECTROLYSIS  RESEARCH 

FURTHER  WORK  NECESSARY  TO  ARRIVE  AT  AN 

ENGINEERING  SOLUTION  OF  THE 

PROBLEM 

The  Committee's  conception  of  an  engineering  solution  of  the 
electrolysis  problem  is  that  the  railway  system  and  the  systems  of 
underground  structures  shall  be  so  designed,  constructed,  main- 
tained, and  operated,  that  the  entire  problem,  caused  by  the 
presence  of  stray  currents  in  the  earth,  including  corrosion  of 
structures,  fire  and  explosion  hazards,  heating  of  power  cables, 
and  operating  losses  and  difficulties,  is  solved  in  the  most  economi- 
cal way. 

1.  Methods  of  Testing. 

The  Research  Sub-committee  of  the  American  Committee  on 
Electrolysis,  in  its  investigations,  has  been  constantly  confronted 
with  the  difficulty  that  available  methods  of  electrolysis  testing  do 
not  yield  directly,  definite  information  as  to  the  electrolytic  con- 
dition of  the  affected  structures.  An  electrolysis  survey,  to  be 
conclusive  must,  in  some  cases,  show  the  true  polarity  of  pipe  or 
cable  with  respect  to  earth  and  in  other  cases  it  must  show  the 
actual  density  of  the  current  flowing  from  pipe  to  earth  in  any 
particular  locality  under  investigation,  but  to  determine  such 
polarity,  or  intensity  of  current  flow,  is  very  difficult.  The  exist- 
ing methods  of  making  electrolysis  surveys  include,  among  others, 
measurements  of  potential  differences  between  pipes  and  earth, 
but  such  measurements,  as  ordinarily  made,  are  often  quite  mis- 
leading. At  the  present  time,  therefore,  the  results  that  follow 
the  application  of  any  particular  method  of  electrolysis  mitiga- 
tion are  sometimes  open  to  question  because  of  the  lack  of  ade- 
quate test  methods.  It  is  evident  therefore,  that  the  development 
of  improved  means  of  electrolysis  testing  whereby  the  actual  cur- 
rent density  of  discharge  from  pipes  to  earth  at  any  point  can  be 
measured  is  an  important  preliminary  step  toward  securing  definite 
information  on  which  the  solution  of  the  outstanding  questions 
relating  to  electrolysis  protection  can  be  based.  The  Research 
Sub-committee  now  has  under  investigation  certain  new  methods 
of  electrolysis  testing  which  offer  considerable  promise  in  this 
direction  and  it  is  felt  that  a  thorough  study  and  development  of 
184 


ELECTROLYSIS  RESEARCH  185 

these  should  be  made  in  the  hope  of  obtaining  improved  test 
methods  and  equipment  that  will  facilitate  securing  the  informa- 
tion required.  It  is  desirable  that  these  investigations  precede 
further  experimental  work  relating  to  methods  of  mitigation. 

2.  Effect  of  Different  Rail  Voltage  Drops. 

It  is  important  to  examine  the  resulting  conditions,  from  an 
electrolysis  standpoint,  of  different  values  of  voltage  drop  in  rails, 
particularly  in  cities  or  localities  where  such  voltage  drops  are 
low,  and  comparable  to  those  which  correspond  to  maximum 
economy  from  the  railway  standpoint,  taking  due  account  of 
variations  in  physical  conditions  in  different  localities. 

3.  Studies  of  Electric  Railway  Power  Distribution. 

Studies  should  be  made  of  the  costs  of  various  measures  de- 
signed to  minimize  track  drops  in  order  to  determine  which 
measures,  if  any,  are  best  to  apply.  The  application  of  auto- 
matic and  semi-automatic  substations  to  street  railways  should 
be  given  consideration  to  determine  how  far  the  voltage  drop 
in  the  rails  can  be  reduced  with  such  a  system  when  developed 
to  the  economic  limit.  In  making  these  cost  studies  track  net- 
works should  be  selected  where  the  layout  is  both  favorable  and 
unfavorable  for  such  installations.  Studies  might  also  be  made 
of  the  joint  application  of  insulated  negative  feeders  and  auto- 
matic substations  to  determine  what  values  of  voltage  drops  in 
the  rails  can  be  obtained  at  reasonable  cost. 

4.  Study  of  Mitigative  Measures  Applicable  to  Affected  Structures. 

After  applying  mitigative  measures  to  the  railway  system,  it 
may  be  found  that  in  many  cases  it  will  still  be  necessary  to  reduce 
further  the  hazards  to  underground  structures.  It  is  therefore 
important  to  study  methods  of  mitigation  applicable  to  the  struc- 
tures themselves,  and  particularly  the  quantitative  effect  of 
insulating  joints  in  protecting  pipes  and  cables  and  the  applica- 
tion and  maintenance  of  such  a  drainage  system  as  will  keep  all 
underground  structures  negative  to  the  earth  without  involving 
fire  and  explosion  hazards,  and  assuming  in  both  cases  the  railway 
stray  current  at  a  low  value. 

5.  Determination  of  Safety  Criterion  for  Pipes  Where  Positive  to 

Earth. 

At  the  present  time  there  is  no  reliable  criterion  as  to  the  actual 
hazard  to  underground  pipes  unless  they  are  at  all  points  negative 
or  neutral  to  earth  at  practically  all  times.  Wherever  pipes  are 


186  ELECTROLYSIS  RESEARCH 

positive  to  earth,  it  is  impossible  with  the  present  methods  of 
testing  to  determine  the  actual  degree  of  corrosion  hazard.  If 
however,  the  development  work  in  connection  with  methods  of 
measuring  current  discharge  from  pipes  mentioned  in  a  preceding 
paragraph  should  result  favorably,  it  appears  probable  that  such 
test  methods  could  be  used  for  the  purpose  of  establishing  a  fairly 
accurate  criterion  for  a  safe  condition  of  underground  structures. 
The  Committee  feels  that  this  question  should  be  investigated 
carefully  so  that  anything  possible  of  accomplishment  in  this 
direction  may  be  realized. 

6.  Self  Corrosion. 

When  iron  pipes  are  embedded  in  certain  soils,  corrosion  due  to 
soil  conditions  or  local  galvanic  action  often  results  in  greater  or 
less  degree.  This  phenomenon  is  commonly  known  as  self  corro- 
sion. Obviously,  it  is  of  importance  to  differentiate  between  the 
effects  of  corrosion  due  to  the  action  of  chemicals  in  the  soil  and 
that  due  to  stray  currents,  in  order  that  an  intelligent  procedure 
can  be  adopted  for  remedying  the  trouble.  It  is  believed  that  a 
thorough  and  systematic  study  of  the  question  of  soil  corrosion 
on  cast  iron,  wrought  iron  and  steel  pipes  would  bring  to  light 
information  that  would  be  of  great  value  in  dealing  with  the 
electrolysis  problem.  Such  investigations  in  order  to  be  of  much 
value  should  be  extended  over  a  period  of  years. 

7.  Fire  and  Explosion  Hazards  on  Gas  and  Oil  Pipes. 

In  addition  to  preventing  corrosion,  there  is  the  closely  related 
problem  of  protecting  against  fires  and  explosions  due  to  electric 
currents  on  gas  or  oil  pipes.  At  the  present  time  no  definite 
information  is  available  as  to  what  limiting  currents  can  safely 
be  permitted  on  such  pipe  systems.  It  is  important  to  investigate 
this  question,  both  statistically  and  experimentally  in  order  to 
evaluate  this  hazard. 

8.  Heating  of  Power  Cables  Due  to  Stray  Currents  on  Sheaths. 

In  view  of  the  fact  that  it  is  common  practice  to  electrically 
drain  the  lead  sheaths  of  power  cables  to  protect  them  from  corro- 
sion, and  since  the  currents  on  the  sheaths  may  be  of  considerable 
magnitude,  reducing  the  current  carrying  capacity  of  the  conduc- 
tors, it  is  important  to  determine  the  limitations  that  should  be 
imposed  on  such  currents  in  order  not  to  cause  serious  heating, 
and  hence  undue  reduction  in  current  carrying  capacity  of  the 
cables. 


ELECTROLYSIS  RESEARCH  187 

Summary.  As  the  Committee  now  views  it,  a  research  of  some 
magnitude  is  necessary  to  secure  further  information  needed  for 
an  engineering  solution  of  the  problem,  to  comprise  the  following: 

1.  Development  of  practical  means  for  measuring  current 
density  across  contact  surfaces  of  pipes  and  earth.     Such 
measurements  are  especially  necessary  if  structures  are  not 
kept  negative  to  earth. 

2.  Development  of  practical  means  for  accurately  deter- 
mining the  polarity  of  structures  and  adjacent  earth,  in  such 
a  way  as  to  eliminate  galvanic  effects. 

3.  Study  of  the  relation  of  different  values  of  voltage  drop 
in  the  track  to  stray  current  from  rails,  including  the  large 
variations  of  this  relation  under  different  conditions,  and  the 
effects  of  such  stray  currents  on  underground  utilities  and 
railway  structures. 

4.  Cost  studies  of  street  railway  systems  and  different 
methods  of  power  supply  to  determine  the  minimum  values 
of  track  voltage  drop  consistent  with  economic  operation  in 
various  locations. 

5.  Quantitative  effect  of  insulating  joints  in  protecting 
pipes  and  cables,  assuming  railway  stray  current  at  low  values. 

6.  Detailed  study  of  the  application  and  maintenance  of 
such  a  drainage  system  as  will  keep  all  underground  struc- 
tures negative  to  earth.     Such  studies  to  include  the  effect 
of  drainage  on  corrosion  of  subsurface  and  railway  structures 
and  its  effect  on  producing  fires  and  explosions. 

7.  Comparison  of  5  and  6. 

8.  Investigation   of  the   distribution   of   current    flowing 
from  pipe  to  adjacent  earth  for  the  purpose  of  determining 
whether  a  diversity  factor  can  be  established,  i.e.,  the  relation 
between  maximum  and  average  current  density. 

9.  Continuing  study  of  joint  corrosion. 

10.  Study  of  soil  and  galvanic  corrosion  with  particular 
reference  to  differentiating  them  from  the  effects  of  stray 
currents. 

11.  Setting  limit  of  current  on  gas  and  oil  pipes  to  avoid 
fire  and  explosion  hazard. 

12.  Setting  limit  of  current  on  power  cable  sheaths  to 
avoid  overheating. 

BIBLIOGRAPHY 

In  compiling  the  following  bibliography  no  attempt  has  been 
made  to  list  the  literature  on  the  subject  of  electrolysis  in  its 


188  ELECTROLYSIS  RESEARCH 

entirety.  This  bibliography  may  be  considered  as  a  selected 
list  of  such  contributions  to  the  subject  known  to  the  committee 
as  in  its  opinion  are  of  the  most  importance  at  the  present  time. 
The  committee,  however,  does  not  sponsor  the  articles  here  listed 
nor  does  it  present  them  as  comprising  a  complete  discussion 
of  the  subject. 

General 

Corrosion  of  Iron  Pipes  by  Action  of  Electric  Railway  Currents. 

Dugald  C.  Jackson.     Journal  of  Association  of  Engineering 

Societies,  September,  1894. 
Electrolytic  Corrosion  of  Iron  by  Direct  Current  in  Street  Soils. 

Albert  F.  Ganz.     Trans.  A.  I.  E.  E.,  Vol.  XXXI,  page  1167. 

1912. 

Stray  Currents  from  Electric  Railways.     Carl  Michalke.     Trans- 
lated and  edited  by  Otis  Allen  Kenyon,  McGraw  Publishing 

Company,  New  York,  N.  Y.     1906. 
Electrolytic  Corrosion  of  Iron  in  Soils.     Burton  McCollum  and 

K.  H.  Logan.     Bureau  of  Standards  Technologic  Paper  No. 

25,  June,  1913. 
Effects   of  Electrolysis   on   Engineering   Structures.     Albert   F. 

Ganz.     Trans.     International    Engineering    Congress,    San 

Francisco,  1915. 

Electrolysis  and  Its  Mitigation.     E.  B.  Rosa  and  Burton  Mc- 
Collum.    Bureau  of  Standards  Technologic  Paper  No.  52, 

Nov.,  1918. 
Electrolysis,  Troubles  Caused  Thereby  and  Remedies  That  May 

be  Applied.     Albert  F.  Ganz,  Journal  New  England  Water 

Works  Association.     Vol.  XXXI,  No.  2,  1917. 
Report  of  Gas  Association  Committee  on  Electrolysis.     J.   D. 

Von  Maur,  Chairman.     Technical  Section  Sessions,  American 

Gas  Association,  1919. 

Electrolytic  Corrosion  of  Pipes  and  Cables 
Destructive  Effect  of  Electric  Currents  on  Subterranean  Metal 

Pipes.     Isaiah  H.  Farnham,  Trans.  A.  I.  E.  E.,  1894. 
Electrolysis  of  Water  Pipes.     Charles  A.  Stone  and  Howard  C. 

Forbes.     New  England  Water  Works  Association,  Vol.  9, 

1894-5. 
Topical  Discussion  on  Electrolysis.     Proc.  New  England  Water 

Works  Association,  Vol.  XX,  1905. 
Earth  Resistance  and  Its  Relation  to  Electrolysis  of  Underground 

Structures.     Burton  McCollum  and  K.  H.  Logan.     Bureau 

of  Standards  Technologic  Paper,  No.  26. 


ELECTROLYSIS  RESEARCH  189 

Surveys  and  Measurements 

Measuring  Stray  Currents  in  Underground  Pipes.  Carl  Hering. 
A.  I.  E.  E.,  June,  1912,  pp.  1147-61. 

Electrolysis  Surveys.  Albert  F.  Ganz.  Engrg.  Rec.,  1908,  V.  57, 
p.  261. 

Methods  of  Making  Electrolysis  Surveys.  Burton  McCollum  and 
G.  H.  Ahlborn,  Bureau  of  Standards  Technologic  Paper  No. 
2&,  1916. 

Bureau  of  Standards  Studies  return  Circuit  Conditions  in  Milwau- 
kee. E.  R.  Shepard.  Elec.  Ry.  Journal,  April  19,  1919,  pp. 
770-772. 

Electrolysis  Surveys  and  Their  Significance.  Report  of  the  1920 
Electrolysis  Committee  of  the  American  Gas  Association, 
L.  A.  Hazeltine,  Chairman.  Technical  Section  Sessions. 

Alternating  Current  and  Periodic  Current  Electrolysis 

Alternating-Current  Electrolysis.  J.  L.  R.  Hay  den.  Trans. 
A.  I.  E.  E.,  1907.  Vol.  26,  part  I. 

Influence  of  Frequency  of  Alternating  or  Infrequently  Reversed 
Current  on  Electrolytic  Corrosion.  Burton  McCollum  and 
G.  H.  Ahlborn.  Bureau  of  Standards  Technologic  Paper 
No.  72,  1916. 

Discussion  of  McCollum  and  Ahlborn  Paper,  New  York.  March 
10,  1916.  Proc.  A.  I.  E.  E.  July,  1916. 

Electrolytic  Corrosion  of  Lead  by  Continuous  and  Periodic  Cur- 
rents. E.  R.  Shepard.  American  Electro-chemical  Society, 
1921. 

Reinforced  Concrete 

Corrosion  of  Iron   Embedded  in   Concrete.     Guy  F.   Schaffer. 

Engineering  Record,  July  30,  1910. 
Electrolytic  Corrosion  of  Iron  and  Steel  in   Concrete.     A.   A. 

Knudson.     Trans.  A.  L  E.  E.,  v.  26,  part  1,  p.  231. 
Electrolysis  in  Concrete.     E.  B.  Rosa,  Burton  McCollum,  and 

O.  S.  Peters.     Bureau  of  Standards  Technologic  Paper  No. 

18,  Mar.,  1913. 
Preventing  Electrolysis  of  Iron  in  Concrete.     W.  A.  Delmar  and 

D.  C.  Woodbury.     Electrical  World,  November  10,  1917. 

Track  Construction,  Track  Leakage,  and  Rail  Bonding 

Modern  Practice  in  the  Construction  and  Maintenance  of  Rail 
Joints  and  Bonds  in  Electric  Railways.  E.  R.  Shepard, 
Bureau  of  Standards  Technologic  Paper  No.  62,  1920. 


190  ELECTROLYSIS  RESEARCH 

Leakage  of  Currents  from  Electric  Railways.     Burton  McCollum 

and  H.  K.  Logan,  Bureau  of  Standards  Technologic  Paper 

No.  63,  1916. 
Data  on  Electric  Railway  Track  Leakage.     G.  H.  Ahlborn,  Bureau 

of  Standards  Technologic  Paper  No.  75,  1916. 
Leakage  Resistance  of  Street  Railway  Roadbeds  and  its  Relation 

to  Electrolysis  of  Underground  Structures.     E.  R.  Shepard. 

Bureau  of  Standards  Technologic  Paper  No.  127.     1919. 

Insulated  Negative  Feeders 

Means  for  Preventing  Electrolysis  of  Buried  Metal  Pipes.  Isaiah 
H.  Farnham.  Cassiers  Magazine,  August,  1895. 

Some  Theoretical  Notes  on  the  Reduction  of  Earth  Currents 
from  Electric  Railway  Systems,  by  Means  of  Negative 
Feeders.  George  I.  Rhodes  Trans.  A.  I.  E.  E.,  Vol.  XXVI, 
p.  247,  1907. 

Special  Studies  in  Electrolysis  Mitigation — II.  E.  B.  Rosa,  Burton 
McCollum  and  K.  H.  Logan.  Bureau  of  Standards  Tech- 
nologic Paper  No.  32,  1913. 

Special  Studies  in  Electrolysis  Mitigation — III.  Burton  McCollum 
and  G.  H.  Ahlborn.  Bureau  of  Standards  Technologic  Paper 
No.  54,  1916. 

Electrolysis  from  Stray  Electric  Currents.  Albert  F.  Ganz. 
Trans.  A.  I.  E.  E.,  Vol.  XXXI,  p.  1167,  1912. 

Automatic  Substations 

Automatic  Substations  on  the  North  Shore  Line.     C.  H.  Jones, 

Electric  Railway  Journal,  Jan.  11,  1919,  53:  84-90. 
Year  of  the  Automatic  Substation  at  Butte.     E.  J.  Nash,  Electric 

Railway  Journal,  March  22,  1919.     53:  565-7. 
Second  Year  of  Automatic  Substation  Operation  at  Butte.     E.  J. 

Nash,  Electric  Railway  Journal,  Jan.  24,  1920.     55:  202. 
Automatic  Railway  Substations.     F.  W.  Peters:  Journal  A.  I.  E.  E 

March,     1920.     39:267-74.     Excerpts    Elec.    Ry.    Journal, 

March   13,   1920.     55:518-19;  Abstract  Elec.   Ry.  Journal, 

June  13,  1920.     55:519-21. 
Experience  Shows  Economy  of  Automatic  Operation.     Electrical 

World,  March  20,  1920. 
Automatic  Stations  for  Heavy  City  Service.     R.   J.   Wensley, 

Journal  A.  I.  E.  E.,  April,  1920.  pp.  359-364. 
Automatic  Substations  at  Des  Moines.     F.  C.  Chambers,  Elec. 

Ry.  Journal,  April  10,  1920,    55:738-44. 


ELECTROLYSIS  RESEARCH  191 

The  Automatic  Substation  in  Electrolysis  Mitigation.  E.  R. 
vShepard,  Electric  Railway  Journal,  April  30,  1921. 

Three- Wire  Operation 

Three-wire  System  in  Los  Angeles.     S.   H.   Anderson,   Electric 

Railway  Journal.     February  26,  1916. 
Line  Drops  and  Rail  Potentials  Reduced  by  Three- Wire  System 

in  Omaha.     E.  H.  Hagensick,  Elec.  Ry.  Journal,  November 

10,  1917. 
Sectionalization   of  Overhead  Wire  for  Three-Wire   Operation. 

E.  R.  Shepard,  Elec.  Ry.  Journal.     December  8,  1917. 
Electrolysis  Mitigation  in  Winnipeg.     W.   Nelson  Smith,  Elec. 

Ry.  Journal,  March  26,  1921. 

Insulating  Pipe  Coverings 

Comparative  Values  of  Various  Coatings  and  Coverings  for  the 
Prevention  of  Soil  and  Electrolytic  Corrosion  of  Iron  Pipe. 
Robert  B.  Harper,  Proc.  Illinois  Gas  Association.  Vol.  5, 
1909.  Also  American  Gas  Light  Journal,  v.  91,  1909. 

Insulation  of  Pipes  as  a  Protection  Against  Electrolysis.     Albert 

F.  Ganz.,  Engineering  Record,  1909,  V.  60,  p.  582.     Also 
Pro.  Am.  Gas  Inst.  about  same  date. 

Surface  Insulation  of  Pipes  as  a  Means  of  Preventing  Electrolysis. 
Burton  McCollum  and  0.  S.  Peters,  Bureau  of  Standards 
Technologic  Paper  No.  15,  1914. 

Insulating  Joints 

Insulating  Couplings  for  Protecting  Pipe  Systems  from  Elec- 
trolysis. William  Brophy  and  A.  R.  Gray,  Am.  Gas  Light 
Journal,  1904,  V.  80,  p.  91. 

Flexible  High  Pressure  Pipe  Joint.  Engrg.  Rec.,  V.  62,  p.  307. 
1910. 

Cement  Joints  for  Cast  Iron  Water  Mains  in  Los  Angeles.  Cement 
World,  February,  1916. 

Pipe  and  Cable  Drainage 

Bonding  Lead  Covered  Cables  to  Prevent  Electrolysis.     W.  G. 

Middleton.     Elec.  Rev.  and  West  Electrn.,  V.  57,  p.  423. 

1910. 
Drainage  if  Necessary  vs.  Negative  Feeder  Electrolysis  Protection. 

D.  W.  Roper,  Elec.  Ry.  Journal,  Dec.  7,  1918. 


192  ELECTROLYSIS  RESEARCH 

Discussion  of  preceding  articles.  Elam  Miller,  H.  C.  Button,  and 
D.  W.  Roper,  Elec.  Ry.  Journal,  April  5,  1919. 

Legal  Aspects 

The  Law  Relating  to  Conflicting  Uses  of  Electricity  and  Electroly- 
sis. George  F.  Deiser.  T.  &  J.  W.  Johnson  Co.,  Phila- 
delphia, Pa.  1911. 

Electrolysis  of  Underground  Conductors.  George  F.  Sever. 
Trans.  International  Electrical  Congress,  Vol.  3,  p.  666.  1904. 


APPENDIX 


TABLE  5 

CURRENT  DATA  FOR  STEEL  RAILS* 

Based  on  a  resistivity  of  0.0003  ohm  per  pound-foot,  this  being  equivalent  to 
about  11  times  the  resistivity  of  copper. 


Weight 
.  (Ibs.  per  yd.) 

Current  for  1m.  v. 
on  1  ft.  (amperes) 

Weight 
(Ibs.  per  yd.) 

Current  for  1  m.  v. 
on  1  ft.  (amperes) 

60 

66.7 

110 

122.0 

65 

72.2 

115 

128.0 

70 

77.8 

120 

133.0 

75 

83.3 

125 

139.0 

80 

88.9 

1      130 

144.0 

85 

94.4 

135 

150.0 

90 

100.0 

140 

156.0 

95 

106.0 

145 

161.0 

100 

111.0 

150 

167.0 

105 

117.0 

*  Does  not  include  rail  joints. 


TABLE  6A 

CURRENT  DATA  FOR  PIPES 
CAST  IRON 


A.W.W.A.  standard 

A.W.W.A.  standard 

Class  A 

Class  B 

Nominal 

inside 

diameter 

Current 

Current 

(inches) 

Weight 

for  1  mv. 

Weight 

for  1  mv. 

pounds 

on  1  ft. 

pounds 

on  1  ft. 

per  foot 

(amperes) 

per  foot 

(amperes) 

3 

13.04 

10.6 

14.60 

11.9 

4 

18.03 

14.7 

20.06 

16.4 

6 

27.90 

22.7 

31.14 

25.4 

8 

38.74 

31.6 

42.68 

34.8 

10 

51.95 

42.3 

58.80 

47.9 

12 

66.90 

55.0 

76.44 

62.0 

14 

82.33 

67.0 

94.82 

77.0 

16 

98.75 

81.0 

114.70 

94.0 

18 

118.10 

96.0 

137.70 

112.0 

20 

137.2 

112.0 

163.20 

133.0 

24 

186.5 

152.0 

217.10 

177.0 

30 

265.1 

216.0 

312.6*0 

255.0 

36 

357.8 

292.0 

419.00 

341.0 

42 

465.6 

379.0 

541.50 

441.0 

48 

607.7 

495.0 

688.50 

562.0 

54 

730.2 

596.0 

842.80 

685.0 

60 

835.6 

680.0 

1,012.00 

826.0 

72 

1,169.0 

952.0 

1,416.00 

1,150.0 

84 

1,141.0 

1,177.0 

1,860.00 

1,515.0 

193 


194 


APPENDIX 


TABLE   6A    (Continued) 
CAST  IRON 


A.W.W.A.  standard 

A.W.W.A.  standard 

Class  C. 

Class  D. 

Nominal 

Inside 

Diameter 

Current 

Current 

(inches) 

Weight 

for  1  mv. 

Weight 

for  1  mv. 

pounds 

on  1  ft. 

pounds 

on  1  ft. 

per  foot 

(amperes) 

per  foot 

(amperes) 

3 

15.47 

12.6 

16.37 

13.2 

4 

21.27 

17.3 

22.83 

18.5 

6 

32.93 

26.8 

35.30 

28.8 

8 

47.97 

39.1 

51.16 

41.7 

10 

65.66 

-     54.0 

71.54 

58.0 

12 

85.26 

70.0 

93.59 

76.0 

14 

108.0 

88.0 

119.1 

97.0 

16 

133.3 

109.0 

147.5 

120.0 

18 

162.4 

132.0 

178.4 

145.0 

20 

190.9 

156.0 

212.4 

173.0 

'24 

257.7 

210.0 

286.2 

233.0 

30 

367.5 

300.0 

421.4 

344.0 

36 

499.8 

407.0 

580.7 

474.0 

42 

656.6 

535.0 

762.0 

621.0 

48 

833.0 

680.0 

960.4 

780.0 

•  I  54 

1,041.0 

848.0 

1,227.0 

1,000.0 

60 

1,220.0 

990.0 

1,458.0 

1,190.0 

72 

1,744.0 

1,430.0 

APPENDIX 


195 


TABLE  6A  (Continued} 
CAST  IRON 


New  England  W.W.A. 

New  England  W.W.A. 

standard  Class  A. 

standard  Class  B. 

•  Nominal 

inside 

diameter 

Current 

Current 

(inches) 

Weight 

for  1  mv. 

Weight 

for  1  mv. 

pounds 

on  1  ft. 

pounds 

on  1  ft. 

per  foot 

(amperes) 

per  foot 

(amperes) 

4 

14  89 

12.1 

6 

24.32 

19  9 

8 

35.58 

29.0 

10 

49.04 

40.0 

52^03 

"42:i' 

12 

61.14 

50.0 

65.92 

54.0 

14 

76.85 

63.0 

82.41 

67.0 

16 

90.98 

74.0 

98.95 

81.0 

18 

104.5 

85.0 

115.2 

94.0 

20 

121.9 

99.0 

133.7 

109.0 

24 

155.6 

127.0 

174.4 

142.0 

30 

215.3 

176.0 

244.8 

200.0 

36 

287.0 

234.0 

326.0 

266.0 

42 

368.4 

300.0 

422.1 

344.0 

48 

459.3 

374.0 

530.2 

432.0 

54 

559.8 

456.0 

650.3 

530.0 

60 

664.0 

541.0 

782.3 

640.0 

196 


APPENDIX 


TABLE  6A   (Continued] 
CAST  IRON 


New  England  W.W.A. 
Standard   Class   C. 

New  England  W.W.A. 
Standard  Class  D. 

Nominal 

Inside 

Diameter 

Current 

Current 

(inches) 

Weight 

for  1  mv. 

Weight 

for  1  mv. 

pounds 

on  1  ft. 

pounds 

on  1  ft. 

per  foot 

(amperes) 

per  foot 

(amperes) 

4 

15.7 

12.8 

6 

26.72 

21.8 

8 

40.38 

32  9 

10 

54.99 

44.8 

57.94 

47.2 

12 

70.67 

58.0 

75.39 

61.0 

14 

87.97 

72.0 

94.85 

77.0 

16 

106.9 

87.0 

114.8 

93.0 

18 

127.4 

104.0 

138.0 

112.0 

20 

147.6 

120.0 

161.4 

132.0 

24 

196.3 

160.0 

215.3 

175.0 

30 

277.7 

226.0 

307.3 

250.0 

36 

373.3 

304.0 

412.3 

336.0 

42 

481.1 

392.0 

538.9 

439.0 

48 

608.0 

495.0 

678.9 

552.0 

54 

749.5 

610.0 

839.9 

684.0 

60 

911.5 

740.0 

1,029.7 

840.0 

APPENDIX 


197 


TABLE  6B 
STEEL    PIPE 


XT               "            1 

Standard 

Extra  Strong 

Nominal 
inside 
diameter 
(inches) 

Weight 
pounds 

Current 
for  1  mv. 
on  1  ft. 

Weight 
pounds 

Current 
for  1  mv. 
on  1  ft. 

per  foot 

(amperes) 

per  foot 

(amperes) 

0.125 

0.24 

1.11 

0.31 

1.44 

0.25 

0.42 

1.95 

0.54 

2.50 

0.375 

0.57 

2.64 

0,74 

3.43 

0.50 

0.85 

3  94 

1  09 

50 

0.75 

1.13 

5.2 

1.47 

6.8 

1  00 

1  68 

7.8 

2.17 

10.1 

1  25 

2.27 

10.5 

3.00 

13.9 

1.50 

2.72 

12.6 

3.63 

16.8 

2.00 

3.65 

16.9 

5.02 

23.3 

2.50 

5.79 

26.8 

7.66 

35.5 

3.00 

7.58 

35.1 

10.25 

47.5 

3.50 

9.11 

42.2 

12.51 

58.0 

4.00 

10.79 

50.0 

14.98 

69.0 

4.50 

12.54 

58.0 

17.61 

82.0 

5.00 

14.62 

68.0 

20.78 

96.0 

6.00 

18.97 

88.0 

28.57 

132.0 

7.00 

23.54 

109.0 

38.05 

176.0 

8.00 

24.70 

114.0 

43.39 

201.0 

8  00 

28  55 

132  0 

9.00 

33.91 

157.0 

"48'73 

226.0 

10.00 

31.20 

145.0 

54.74 

254.0 

10.00 

34.24 

159.0 

10.00 

40.48 

188.0 

11.00 

45.56 

211.0 

60.08 

278.0 

12.00 

43.77 

203.0 

65.42 

303.0 

12.00 

49.56 

230.0 

13.00 

54.57 

253.0 

72.09 

334.0 

14.00 

58.57 

271.0 

77.43 

359.0 

15.00 

62.58 

290.0 

82.77 

383.0 

198 


APPENDIX 


TABLE  *6C 
WROUGHT  IRON  PIPE 


Standard 

Extra    Strong 

Nominal 
Inside 
diameter 
(inches) 

Weight 
pounds 

Current 
for  1  mv. 
on  1  ft. 

Weight 
pounds 

Current 
for  1  mv. 
on  1  ft. 

per  foot 

(amperes) 

per  foot 

(amperes) 

0.125 

0.24 

1.15 

0.29 

1.39 

0.25 

0.42 

2  01 

0.54 

2.58 

0.375 

0.56 

2.68 

0.74 

3.54 

0.50 

0.84 

4.02 

1.09 

5.2 

0.75 

1  12 

5.4 

1.39 

6.6 

1.0 

1.67 

8.0 

2.17 

10.4 

1,25 

2.25 

10.8 

3.00 

14.3 

1.50 

2.69 

12.9 

3.63 

17.4 

2.0 

3.66 

17.5 

5.02 

24.0 

2.50 

5.77 

27.6 

7.67 

36.7 

3.0 

7.54 

36.0 

10.25 

49.0 

3.50 

9.05 

43.3 

12.47 

60.0 

4.0 

10.72 

51.0 

14.97 

72.0 

4.50 

12.49 

60.0 

18.22 

87.0 

5.0 

14.56 

70.0 

20.54 

98.0 

6.0 

18.76 

90.0 

28.58 

137.0 

7.0 

23.41 

112.0 

37.67 

180.0 

8.0 

25.00 

120.0 

43.00 

206.0 

8.0 

28.34 

136.0 

9.0 

33.70 

161.0 

48.73 

233.0 

10.0 

32  00 

153  0 

10.0 

35.00 

167.0 

10.0 

40.00 

191.0 

"54^74 

"262.Q 

11.0 

45.00 

215.0 

60.08 

287.0 

12  0 

45  00 

215  0 

12.0 

49.00 

234.0 

65.42 

313.0 

APPENDIX 


199 


TABLE    6D 
A.  G.   I.   Standard  Gas 


Nominal  inside 
diameter  (inches) 

Weight  pounds 
per  foot 

Current  for   1  mv. 
on  1  ft.  (amperes) 

4 

17.3 

14.1 

6 

27.3 

22.2 

8 

38.0 

30.9 

10 

51.  0* 

41.5 

12 

67.0 

55.0 

16 

102.0 

83.0 

20 

139.0 

113.0 

24 

186.0 

152.0 

30 

256.0 

209.0 

36 

346.0 

282.0 

42 

453.0 

369.0 

48 

610.0 

405.0 

TABLE  6E 
LEAD  PIPE 


Current  for 

Specimen  No. 

Card   diameter 
(inches) 

Card  weight 
(Ibs.  per  ft.) 

1  mv.  drop  per 
^foot   (amperes) 

1 

0.25 

0.5 

0.915 

2 

.25 

.5 

.908 

3 

.25 

.5 

.942 

4 

.75(AA) 

3.5 

7.257 

5 

.75(AA) 

3.5 

7.332 

6 

.75(AA) 

3.5 

7.305 

7 

.75(AA) 

3.5 

7.123 

8 

.75(AA) 

3.5 

7.148 

9 

.75(AA) 

3.5 

7.067 

10 

.00(C) 

2.5 

4.914 

11 

.00(C) 

2.5 

4.921 

12 

.00(C) 

2.5 

4.958 

13 

.00  (A  A) 

4.75 

9.785 

14 

.OO(AA) 

4.75 

9.833 

15 

.OO(AA) 

4.75 

9.766 

16 

2.00(C) 

6.0 

11.81 

17 

2.00(C) 

6.0 

11.78 

18 

2.00(C) 

6.0 

11.77 

19 

2.00(AA) 

9.0 

18.14 

20 

2.00(AA) 

9.0 

18.11 

21 

2.00(AA) 

9.0 

18.11 

22 

.25 

.5 

.915 

23 

.25 

.5 

.913 

24 

.25 

.5 

.915 

25 

.75(C) 

1.75 

3.302 

26 

•  75(C) 

1.75 

3.343 

27 

.75(C) 

1.75 

3.322 

200 


APPENDIX 


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202 


APPENDIX 


POTENTIAL     MEASUREMENTS 


II- 


APPENDIX 


203 


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204 


APPENDIX 


1 1 

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III 

II 


Engineering 
Library 


xv- % 


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